# Think Python/Answers


## Chapter 1

See below for Chapter 1 exercises.

### Exercise 1.2

1.) How many seconds are there in 42 minutes 42 seconds?

\>\>\> (42 \* 60) + 42

**2562 seconds**

2.) How many miles are there in 10 kilometers? Hint there are 1.61
kilometers in a mile.

\>\>\> 10/1.61

**6.21 miles**

3.) If you run a 10 kilometer race in 42 minutes 42 seconds, what is
your average time per mile? What is your average speed in miles per
hour? (Hint: there are about 1.61 kilometers in a mile.)

\>\>\> 10 / 1.61 \# convert kilometers to miles

6.211180124223602

\>\>\> (42 \* 60) + 42 \# convert time to seconds

2562

\>\>\> 2562 / 6.211180124223602 \# what is your average time (seconds)
per mile

412.482

\>\>\> 412.482 / 60 \# what is your average time (minutes) per mile

**6.874700000000001**

\>\>\> 60 / 6.874700000000001 \# miles per hour

**8.727653570337614**

How about another way

\>\>\> 10 / 42.7 \# avg kilometers per minute

0.23419203747072598

\>\>\> 0.23419203747072598 \* 60 \# kilometers per hour

14.05152224824356

\>\>\> 14.05152224824356 / 1.61 \# convert to M.P.H

8.727653570337614

or a one-liner

\>\>\> (10 / 1.61) / (42.7 / 60) \# (distance in miles) / (time in
hours)

8.727653570337614 \# miles/hour

## Chapter 2

### Exercise 2.1

If you type an integer with a leading zero, you might get a confusing
error:

``` python
>>> zipcode = 02492
                  ^
SyntaxError: invalid token
```

Other number seem to work, but the results are bizarre:

``` python
>>> zipcode = 02132
>>> print zipcode
1114
```

So python is assuming you want to convert an octal number to a decimal
number. In the base 8 numbering system where valid numbers are **0, 1,
2, 3, 4, 5, 6 and 7**.

``` python
Base  8: 00 01 02 03 04 05 06 07 10 11 12 13 14 15 16 17 20 21 22 23 24
Base 10: 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20
```

Every 8 numbers we increment the left hand columns. This means that the
right most column is the number of \'ones\'. The one to the left of that
is a tally of the number of \'eights\', the one next to that is a tally
of a full column of \'eight\' times the \'eight column\' - 64. The one
next to that is 64\*8 - 512 and so on. For more information read Base
Eight math.

That is why **zipcode = 02492** is invalid as the digit 9 is not a valid
octal number. We can do the conversion manually as follows:

``` python
>>> print 02132
1114
>>> (2*512)+(1*64)+(3*8)+(2*1)
1114
>>> 
```

### Exercise 2.2

The volume of a sphere with radius **r** is *4/3* π *r*^*3*^\'\'. What
is the volume of a sphere with radius 5?

``` python
>>> pi = 3.1415926535897932
>>> r = 5
>>> 4/3*pi*r**3 # This is the wrong answer
392.69908169872411
>>> r = 5.0 # Radius can be a float here as well, but is not _necessary_.
>>> 4.0/3.0*pi*r**3 # Using floats give the correct answer
523.5987755982989
>>> 
```

Suppose the cover price of a book is \$24.95, but bookstores get a 40%
discount. Shipping costs \$3 for the first copy and 75 cents for each
additional copy. What is the total wholesale cost for 60 copies?\'\'

``` python
 $24.95  Cost
  $9.98  Discount per book
 $14.97  Cost per book after discount
  60     Total number of books
$898.20  Total cost not inc delivery

  $3.00  First book delivery
  59     Remaining books
  $0.75  Delivery cost for extra books
 $44.25  Total cost for extra books
 $47.25  Total Delivery cost
    
$945.45  Total Bill

This answer is wrong because 40.0/100.0 return wrong value 0.40000000000000002 for more info see IEEE 754 (Standard for Floating-Point Arithmetic)
>>> (24.95-24.95*40.0/100.0)*60+3+0.75*(60-1)
945.44999999999993
>>> 24.95*0.6*60+0.75*(60-1)+3
945.45

You can use the decimal module to maintain precision.
from decimal import Decimal
..
...
def wholesale_cost(args):

    d = 1 - args.get('discount')/100 
    purchase = Decimal(args.get('cost') * d * 60)
    return purchase + Decimal(args.get('delivery'))

args =  {'cost': 24.95, 'discount': 40, 'delivery': 3.00+0.75*59}
```

Another solution using functions as well as input prompts:

``` python
# Total wholesale book cost calculator
cover_price = 24.95

number_of_books = int(input("How many books do you want to order at wholesale? "))

def ship_cost (number_of_books):
    if number_of_books == 1:
        return (number_of_books * 3) # Cost of shipping one book is $3
    else:
        return (3 + (number_of_books - 1) * 0.75) # Each additional copy of the book is $0.75 to ship

def discounted_price(number_of_books):
    return(cover_price - (cover_price * .4)) # There is a 40% discount on wholesale book sales

def wholesale_cost(number_of_books):
    return ((discounted_price(number_of_books) * number_of_books) + ship_cost(number_of_books))

print("The cost of buying and shipping", number_of_books, "books is $",round(wholesale_cost(number_of_books), 2))
```

If I leave my house at 6:52 am and run 1 mile at an easy pace (8:15 per
mile), then 3 miles at tempo (7:12 per mile) and 1 mile at easy pace
again, what time do I get home for breakfast?

Answer: **7:30 am**

How I did it:

``` python
>>> start = (6*60+52)*60
>>> easy = (8*60+15)*2
>>> fast = (7*60+12)*3
>>> finish_hour = (start + easy + fast)/(60*60.0)
>>> finish_floored = (start + easy + fast)//(60*60)  #int() function can also be used to get integer value, but it hasn't taught yet.
>>> finish_minute  = (finish_hour - finish_floored)*60
>>> print ('Finish time was %d:%d' % (finish_hour,finish_minute))
Finish time was 7:30

*** ANOTHER WAY ***
start_time_hr = 6 + 52 / 60.0
easy_pace_hr = (8 + 15 / 60.0 ) / 60.0
tempo_pace_hr = (7 + 12 / 60.0) / 60.0
running_time_hr = 2 * easy_pace_hr + 3 * tempo_pace_hr
breakfast_hr = start_time_hr + running_time_hr
breakfast_min = (breakfast_hr-int(breakfast_hr))*60
breakfast_sec= (breakfast_min-int(breakfast_min))*60

print ('breakfast_hr', int(breakfast_hr) )
print ('breakfast_min', int (breakfast_min) )
print ('breakfast_sec', int (breakfast_sec) )
>>> 
```

## Chapter 3

### Exercise 3.1

Python provides a built-in function called *len* that returns the length
of a string, so the value of len(\'allen\') is 5. Write a function named
right_justify that takes a string named *s* as a parameter and prints
the string with enough leading spaces so that the last letter of the
string is in column 70 of the display.

``` python
>>> def right_justify(s):
     print (' '*(70-len(s))+s)
 
>>> right_justify('allen')
                                                                 allen
>>> 
```

Alternate Solution Using concatenation and repetition

``` python

def right_justify(s):
    total_length = 70
    current_length = len(s)
    current_string = s
    while current_length < total_length:
       current_string = " " + current_string
       current_length = len(current_string)
    print(current_string)

OUTPUT

>>> right_justify("monty")
                                                                 monty
```

### Exercise 3.3

You can see my solution at <http://thinkpython.com/code/grid.py>.

``` python
"""
Solution to Exercise 3.5 on page 27 of Think Python
Allen B. Downey, Version 1.1.24+Kart [Python 3.2]

"""

# here is a mostly-straightforward solution to the
# two-by-two version of the grid.

def do_twice(f):
    f()
    f()

def do_four(f):
    do_twice(f)
    do_twice(f)

def print_beam():
    print('+ - - - -', end='')

def print_post():
    print('|        ', end='')

def print_beams():
    do_twice(print_beam)
    print('+')

def print_posts():
    do_twice(print_post)
    print('|')

def print_row():
    print_beams()
    do_twice(print_posts)

def print_grid():
    do_twice(print_row)
    print_beams()

print_grid()
 ____________   

# another solution

def do_twice(f):
    f()
    f()

def do_four(f):
    do_twice(f)
    do_twice(f)

def print_column():
    print '+----+----+'

def print_row():
    print '|    |    |'

def print_rows():
    do_four(print_row)

def do_block():
    print_column()
    print_rows()

def print_block():
    do_twice(do_block)
    print_column()

print_block()

# nathan moses-gonzales
_________

# straight-forward solution to 4x4 grid

def do_twice(f):
    f()
    f()

def do_four(f): # not needed for 2x2 grid
    do_twice(f)
    do_twice(f)

def print_beam():
    print('+----', end='')

def print_post():
    print('|    ', end='')

def print_beams():
    do_twice(print_beam)
    print('+')

def print_posts():
    do_twice(print_post)
    print('|')

def print_row():
    print_beams()
    do_twice(print_posts)

def print_grid2x2():
    do_twice(print_row)
    print_beams()

def print_beam4():
    do_four(print_beam)
    print('+')

def print_post4():
    do_four(print_post)
    print('|')

def print_row4():
    print_beam4()
    do_twice(print_post4)

def print_grid4x4():
    do_four(print_row4)
    print_beam4()

print_grid4x4()
-----------------------

# here is a less-straightforward solution to the
# four-by-four grid 

def one_four_one(f, g, h):
    f()
    do_four(g)
    h()

def print_plus():
    print '+',

def print_dash():
    print '-',

def print_bar():
    print '|',

def print_space():
    print ' ',

def print_end():
    print

def nothing():
    "do nothing"

def print1beam():
    one_four_one(nothing, print_dash, print_plus)

def print1post():
    one_four_one(nothing, print_space, print_bar)

def print4beams():
    one_four_one(print_plus, print1beam, print_end)

def print4posts():
    one_four_one(print_bar, print1post, print_end)

def print_row():
    one_four_one(nothing, print4posts, print4beams)

def print_grid():
    one_four_one(print4beams, print_row, nothing)

print_grid()

comment = """
After writing a draft of the 4x4 grid, I noticed that many of the
functions had the same structure: they would do something, do
something else four times, and then do something else once.

So I wrote one_four_one, which takes three functions as arguments; it
calls the first one once, then uses do_four to call the second one
four times, then calls the third.

Then I rewrote print1beam, print1post, print4beams, print4posts,
print_row and print_grid using one_four_one.

Programming is an exploratory process.  Writing a draft of a program
often gives you insight into the problem, which might lead you to
rewrite the code to reflect the structure of the solution.

--- Allen
"""

print comment

# another solution
def beam():
    plus = "+"
    minus = "-"*4
    print(plus, minus, plus,minus, plus, minus, plus, minus, plus)

def straight():
    straight = "|"
    space = " "*4
    print(straight, space, straight, space, straight, space, straight, space,
          straight, space)

def quad_straight():
    straight()
    straight()
    straight()
    straight()

def twice():
    beam()
    quad_straight()
    beam()
    quad_straight()

def quad():
    twice()
    twice()
    beam()

quad()
-- :)
------------------

# Without functions. 
print("+ - - - - " * 2 + "+")
print("|\t\t  | \t\t|\n" * 3 + "|\t\t  | \t\t|")
print("+ - - - - " * 2 + "+")
print("|\t\t  | \t\t|\n " *3 + "|\t\t  | \t\t|")
print("+ - - - - " * 2 + "+")

------------------

Why not using the first solution and adapt it to the number of rows

def do_twice(f):
    f()
    f()

def do_four(f):
    do_twice(f)
    do_twice(f)

def print_column():
    print '+----+----+----+----+'

def print_row():
    print '|    |    |    |    |'

def print_rows():
    do_four(print_row)

def do_block():
    print_column()
    print_rows()

def print_block():
    do_twice(do_block)
    # print_column()
    do_twice(do_block)
    print_column()

print_block()


-----------------------
# mteodor

def draw_line(bar, middle = ' ', repeat = 2, length = 2):
  """ Draw a single line like this:
  [ (B M*repeat)*length B]
  """
  for k in range(length):
    print("%s %s " % (bar, middle*repeat), end='')
  print(bar)

def draw_grid(length = 2, height = 2, width = 2):
  """ Draw a grid like this:
  + -- + -- +
  |    |    |
  |    |    |
  + -- + -- +
  |    |    |
  |    |    |
  + -- + -- +
  where:
  * length x height are the table size
  * width is the size of a cell/column
  """
  for i in range(height):
    draw_line('+', '-', width, length)
    for j in range(length):
      draw_line('|', ' ', width, length)
  draw_line('+', '-', width, length)

draw_grid(4, 4, 3)


--------------------------
#kipp

# auto adjust size of columns

size=4

def beam():
    print(" + - - - -"*size, "+")

def post():
    print(" |        "*size, "|")

def repeat(func):
    func()
    func()
    func()

# manual adjust size for rows
# this is 4

beam()
repeat(post)
beam()
repeat(post)
beam()
repeat(post)
beam()
repeat(post)
beam()
```

## Chapter 4

### 4.3 Exercise 1

``` python
from TurtleWorld import *

world = TurtleWorld()
bob = Turtle()

def square(t):
    for i in range(4):
        fd(t, 100)
        lt(t)

square(bob)
wait_for_user()
```

### 4.3 Exercise 2

``` python
from TurtleWorld import *

world = TurtleWorld()
bob = Turtle()
print(bob)

def square(t, length):
    t = Turtle()
    for i in range(4):
        fd(t, length)
        lt(t)

square(bob, 200)
wait_for_user()
```

### 4.3 Exercise 3

``` python
from swampy.TurtleWorld import *

world = TurtleWorld()
bob = Turtle()
print(bob)

def polygon(t, length, n):
    
    for i in range(n):
        fd(t, length)
        lt(t, 360 / n)

polygon(bob, 50, 8)
wait_for_user()
```

## Chapter 5

### Exercise 5.2

``` python
def countdown(a):         # A typical countdown function
    if a < 0:
        print("Blastoff")
    elif a > 0:
        print(a)
        countdown(a - 1)

def call_function(n,a):    # The countdown function is called "n" number of times. Any other function can be used instead of countdown function.
    for i in range(n):
        countdown(a)
    
call_function(3, 10)
```

### Exercise 5.3

``` python
def is_triangle(a, b, c):
       if a <= b+c:
            if b <= a+c:
                 if c <= a+b:
                    return 'yes'
                 else:
                    return 'no'
            else:
                 return 'no'
       else:
            return 'no'

is_triangle(1, 12, 1)
'no'
```

### Exercise 5.3

``` python
def is_triangle(a, b, c):
       if a<=b+c and b<=a+c and c<=a+b:
           return 'yes'
       else:
           return 'no'

is_triangle(1, 12, 3)
'no'
```

## Chapter 9

### Exercise 9.1

``` python

fin = open('words.txt')
for line in fin:
    word = line.strip()
    if len(word) > 20:
        print (word)
```

### Exercise 9.2

``` python

fin = open('words.txt')

def has_no_e(word):
    for char in word:
        if char in 'Ee':
            return False
    return True  

count = 0
for line in fin:
    word = line.strip()
    if has_no_e(word):
        count += 1
        print (word)

percent = (count / 113809.0) * 100

print (str(percent)) + "% of the words don't have an 'e'."
```

### Exercise 9.3

``` python

fin = open('words.txt')

def avoids(word,letter):
    for char in word:
        if char in letter:
            return False
    return True


letter = raw_input('What letters to exclude? ')
count = 0
for line in fin:
    word = line.strip()
    if avoids(word, letter):
        count += 1
        print word

percent = (count / 113809.0) * 100

print str(percent) + "% of the words don't have " + letter + '.'
```

### Exercise 9.4

``` python
def uses_only(word, letters):
    """returns true if word is made only out of letters  else flase"""
    for letter in word:
        if letter not in letters:
            return False
    return True
```

## Chapter 10

### Exercise 10.1

Write a function called nested_sum that takes a nested list of integers
and add up the elements from all of the nested lists.

``` python
def nested_sum(nestedList):
        '''
        nestedList: list composed of nested lists containing int.
        Returns the sum of all the int in the nested list
        '''
        newList = []
        #Helper function to flatten the list
        def flatlist(nestedList):
                '''
                Returns a flat list
                '''
                for i in range(len(nestedList)):
                        if type(nestedList[i]) == int:
                                newList.append(nestedList[i])
                        else:
                                flatlist(nestedList[i])
                return newList

        flatlist(nestedList)
        print sum(newList)
        
nested_sum(nestedList)
```

### Exercise 10.2

Write a function named \"capitalize_nested\" that takes a nested list of
strings and returns a new nested list with all strings capitalized.

``` python
>>> def capitalize_nested(l): 
        def capitalize(s):
            return s.capitalize()
        for n, i in enumerate(l):       
            if type(i) is list:
                l[n] = capitalize_nested(l[n])
            elif type(i) is str:
                l[n] = capitalize(i)
        return l
```

### Exercise 10.3

Write a function that takes a list of numbers and returns the cumulative
sum.

``` python
>>> def cumulative(l):
    cumulative_sum = 0
    new_list = []
    for i in l:
        cumulative_sum += i
        new_list.append(cumulative_sum)
    return new_list
```

### Exercise 10.4

Write a function called middle that takes a list and returns a new list
that contains all but the first and last elements.

``` python
>>> def middle(x):
    res = []
    i = 1
    while i <= len(x)-2:
        res.append(x[i])
        i += 1
    return res
```

This can also be done simply with a slice.

``` python
>>> def middle(x):
        return x[1:-1]
```

### Exercise 10.5

Write a function called chop that takes a list and modifies it, removing
the first and last elements, and returns None.

``` python
>>> def chop(x):
        del x[:1]
        del x[-1:]
```

## Chapter 11

### Exercise 11.1

Write a function that reads the words in words.txt and stores them as
keys in a dictionary. It doesn't matter what the values are. Then you
can use the in operator as a fast way to check whether a string is in
the dictionary.

``` python
fin = open('words.txt')
englishdict = dict()


def create_diction():
    counter = 0
    dictionairy = dict()
    for line in fin:
        word = line.strip()
        dictionairy[word] = counter
        counter += 1
    return dictionairy
```

### Exercise 11.2

``` python
def invert_dict(s):
    i={}
    for key in s:
        v=s[key]
        i.setdefault(v, []).append(key)
    return i
```

Edit: This was not the exercise I found in my edition of \'Think
Python\', so I\'ve added my answer in case anyone else is curious: Use
get to write histogram more concisely. You should be able to eliminate
the if statement.

``` python
def histogram(s):
    d = dict()
    for c in s:
        d[c] = d.get(c,0)+1
    return d
```

### Exercise 11.3

Dictionaries have a method called keys that returns the keys of the
dictionary, in no particular order, as a list. Modify print_hist to
print the keys and their values in alphabetical order.

``` python
v = {'p' : 1, 'a' : 1, 'r' : 2, 'o' : 1, 't' : 1}
def print_hist(h):
    d = []
    d += sorted(h.keys())
    for c in d:
        print(c, h[c])
```

OR

``` python
v = {'p' : 1, 'a' : 1, 'r' : 2, 'o' : 1, 't' : 1}
def print_hist(h):
    for c in sorted(h.keys()):
        print c, h[c]
```

### Exercise 11.4

Modify reverse_lookup so that it builds and returns a list of all keys
that map to v, or an empty list if there are none.

``` python
def reverse_lookup(d,v):
    l = list()
    for c in d:
        if d[c] == v:
            l.append(c)
    return l
```

## Chapter 12

### Exercise 12.1

``` python
numbers = (1,2,3)
def sumall(numbers):
    x = 0
    for i in numbers:
        x = x + i
    print x
sumall(numbers)
```

or

``` python
def sumall(*t):
    x = 0
    for i in range(len(t)):
        x += t[i]
    return x
```

or

``` python
def sumall(*args):
    t = list(args)
    return sum(t)
```

or

``` python
def sumall(*args):
    return sum(args)
```

### Exercise 12.2

``` python
import random

def sort_by_length(words):
    t = []
    for word in words:
        t.append((len(word),word))
    t.sort(reverse=True)
    res = []
    for length, word in t:
        res.append(word)
    i=0
    final = []
    while i <= len(res)-2:
        if len(res[i]) == len(res[i+1]):
            y_list = [res[i], res[i+1]]
            random.shuffle(y_list)
            final = final + y_list
            i += 2
        else:
            final.append(res[i])
            i += 1
    if i == len(res)-1:
        final.append(res[i])
    return final
```

or

``` python
from random import shuffle

def sort_by_length(words):
    r = []
    d = dict()
    for word in words:
        d.setdefault(len(word), []).append(word)
    for key in sorted(d, reverse=True):
        if len(d[key]) > 1:
            shuffle(d[key])
        r.extend(d[key])
    return r
```

### Exercise 12.3

``` python
import string

def most_frequent(s):
    d = dict()
    inv = dict()
    for char in s:
        if char in string.ascii_letters:
            letter = char.lower()       
            d[letter] = d.get(letter, 0) + 1
            
    for letter, freq in d.items():
        inv.setdefault(freq, []).append(letter)
        
    for freq in sorted(inv, reverse=True):
        print('{:.2%}:'.format(freq/(sum(list(inv)*len(inv[freq])))), ', '.join(inv[freq]))
```

## Chapter 13

### Exercise 13.7

``` python
from string import punctuation, whitespace, digits
from random import randint
from bisect import bisect_left

def process_file(filename):
    h = dict()
    fp = open(filename)
    for line in fp:
        process_line(line, h)
    return h

def process_line(line, h):
    line = line.replace('-', ' ')
    for word in line.split():
        word = word.strip(punctuation + whitespace + digits)
        word = word.lower()
        if word != '':
            h[word] = h.get(word, 0) + 1

hist = process_file('emma.txt')

def cum_sum(list_of_numbers):
    cum_list = []
    for i, elem in enumerate(list_of_numbers):
        if i == 0:
            cum_list.append(elem)
        else:
            cum_list.append(cum_list[i-1] + elem)
    return cum_list

def random_word(h):
    word_list = list(h.keys())
    num_list = []
    for word in word_list:
        num_list.append(h[word])
    cum_list = cum_sum(num_list)
    i = randint(1, cum_list[-1])
    pos = bisect_left(cum_list, i)
    return word_list[pos]

print(random_word(hist))
```

## Chapter 14

### Exercise 14.3

``` python
import shelve

def dict_of_signatures_and_words(filename='words.txt'):
    d = dict()
    for line in open(filename):
        word = line.lower().strip()
        signature = ''.join(sorted(word))
        d.setdefault(signature, []).append(word)
    return d

def db_of_anagrams(filename='anagrams', d=dict_of_signatures_and_words()):
    db = shelve.open(filename)
    for key, values in d.items():
        if len(values)>1:
            for index, value in enumerate(values):
                db[value]=values[:index]+values[index+1:]
    db.close()

def print_contents_of_db(filename='anagrams'):
    db = shelve.open(filename, flag='r')
    for key in sorted(db):
        print(key.rjust(12), '\t<==>\t', ', '.join(db[key]))
    db.close()

db_of_anagrams()
print_contents_of_db()
```

### Exercise 14.5

``` python
# Replace urllib.request with urllib if you use Python 2.
# I would love to see a more elegant solution for this exercise, possibly by someone who understands html.

import urllib.request

def check(zip_code):
    if zip_code == 'done':
        return False
        
    else:
                if len(zip_code) != 5:
              print('\nThe zip code must have five digits!')
        return True

def get_html(zip_code):
    gibberish = urllib.request.urlopen('http://www.uszip.com/zip/' + zip_code)
    less_gib = gibberish.read().decode('utf-8')
    return less_gib

def extract_truth(code, key, delimiter):
    pos = code.find(key) + len(key)
    nearly_true = code[pos:pos+40]
    truth = nearly_true.split(delimiter)[0]
    return truth

while True:
    zip_code = input('Please type a zip code (5 digits) or "done" if want to stop:\n')
    
    if not check(zip_code):
                 break
    
    code = get_html(zip_code)
    
    invalid_key = '(0 results)'
    if invalid_key in code:
        print('\nNot a valid zip code.')
        continue
    
    name_key = '<title>'
    name_del = ' zip'
    name = extract_truth(code, name_key, name_del)
    
    pop_key = 'Total population</dt><dd>'
    pop_del = '<'
    pop = extract_truth(code, pop_key, pop_del)
    
    if not 1 < len(pop) < 9:
        pop = 'not available'

    print('\n' + name)
    print('Population:', pop, '\n')
```

## Chapter 15

### Exercise 15.1

``` python
import math

class Point(object):
    """represents a point in 2-D space"""

def distance(p1, p2):
    distance = math.sqrt((p2.x - p1.x)**2 + (p2.y - p1.y)**2)
    return distance

p1 = Point()
p2 = Point()

p1.x = 3
p1.y = 2
p2.x = 4
p2.y = 3

print(distance(p1, p2))
```

### Exercise 15.3

``` python

import copy

def move_rectangle(rec, dx, dy):
    """ does a deep copy and return the newRec with changes applied """
    newRec = copy.deepcopy(rec)
    newRec.corner.x += dx
    newRec.corner.y += dy

    return newRec
```

## Chapter 16

### Exercise 16.1

``` python
def print_time(t):
    print '%.2d:%.2d:%.2d' % (t.hour, t.minute, t.second)
```

or

``` python
# Solution for Python3
# More on string formatting: http://docs.python.org/py3k/library/string.html#formatspec

def print_time(t):
    # 0 is a fill character, 2 defines the width
    print('{}:{:02}:{:02}'.format(t.hour, t.minute, t.second))
```

### Exercise 16.2

``` python
def is_after(t1, t2):
    return (t1.hour, t1.minute, t1.second) > (t2.hour, t2.minute, t2.second)
```

### Exercise 16.3

``` python
# Comment not by the author: This will give a wrong result, if (time.second + seconds % 60) > 60

def increment(time, seconds):

    n = seconds/60
    time.second += seconds - 60.0*n
    time.minute += n

    m = time.minute/60
    time.minute -= m*60
    time.hour += m
```

or

``` python
# Solution for Python3
# Replace '//' by '/' for Python2

def increment(time, seconds):
    time.second += seconds
    time.minute += time.second//60
    time.hour += time.minute//60
    
    time.second %= 60
    time.minute %= 60
    time.hour %= 24
```

``` python
# A different way of going about it

def increment(time, seconds):
    # Converts total to seconds, then back to a readable format
    time.second = time.hour*3600 + time.minute*60 + time.second + seconds
    (time.minute, time.second) = divmod(time_in_seconds, 60)
    (time.hour, time.minute) = divmod(time.minute, 60)
```

### Exercise 16.4

``` python
# Solution for Python3
# Replace '//' by '/' for Python2

from copy import deepcopy

def increment(time, seconds):
    r = deepcopy(time)
    
    r.second += seconds
    r.minute += r.second//60
    r.hour += r.minute//60
    
    r.second %= 60
    r.minute %= 60
    r.hour %= 24

    return r
```

### Exercise 16.5

``` python
class Time(object):
    """represents the time of day.
        attributes: hour, minute, second"""

time = Time()
time.hour = 11
time.minute = 59
time.second = 30

def time_to_int(time):
    minutes = time.hour * 60 + time.minute
    seconds = minutes * 60 + time.second
    return seconds

def int_to_time(seconds):
    time = Time()
    minutes, time.second = divmod(seconds, 60)
    time.hour, time.minute = divmod(minutes, 60)
    return time

def increment(time, addtime):
    seconds = time_to_int(time)
    return int_to_time(seconds + addtime)

def print_time (x):
    print 'The time is %.2d : %.2d : %.2d' % (x.hour, x.minute, x.second)
print_time (time)

newtime = increment (time, 70)

print_time (newtime)
```

### Exercise 16.6

``` python
def time_to_int(time):
    minutes = time.hour * 60 + time.minute
    seconds = minutes * 60 + time.second
    return seconds

def int_to_time(seconds):
    time = Time()
    minutes, time.second = divmod(seconds, 60)
    time.hour, time.minute = divmod(minutes, 60)
    return time

def mul_time(time, factor):
    seconds = time_to_int(time)
    seconds *= factor
    seconds = int(seconds)
    return int_to_time(seconds)
    
def average_pace(time, distance):
    return mul_time(time, 1/distance)
```

### Exercise 16.7

Write a class definition for a Date object that has attributes *day*,
*month* and *year*. Write a function called *increment_date* that takes
a Date object, *date*, and an integer, *n*, and returns a new Date
object that represents the day *n* days after *date*. Hint: "Thirty days
hath September\..." Challenge: does your function deal with leap years
correctly? See *wikipedia.org/wiki/Leap_year*.

``` python
class Date(object):
    """represents a date.
    attributes: day, month, year"""

def print_date(date):
    # German date format

    print('{}.{}.{}'.format(date.day, date.month, date.year))

def is_leap_year(year):
        # http://en.wikipedia.org/wiki/Leap_year#Algorithm

    if year % 4 == 0:
        if year % 100 == 0:
            if year % 400 == 0:
                return True
            return False
        return True
    return False

def month_list(year):
    if is_leap_year(year):
        return [31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]
    return [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]

def days_of_year(year):
    if is_leap_year(year):
        return 366
    return 365

def date_to_int(date):
    days = 0
    for year in range(1, date.year):
        days += days_of_year(year)
    
    month_days = month_list(date.year)
    for month in range(1, date.month):
        days += month_days[month - 1]
    
    days += date.day - 1
    return days

def int_to_date(days):
    date = Date()
    
    date.year = 1
    next_days = 365
    while days >= next_days:
        date.year += 1
        days -= next_days
        next_days = days_of_year(date.year)
        
    date.month = 1
    next_days = 31
    month_days = month_list(date.year)
    while days >= next_days:
        date.month += 1
        days -= next_days
        next_days = month_days[date.month - 1]
    
    date.day = days + 1
    return date

def increment_date(date, n):
    days = date_to_int(date)
    return int_to_date(days + n)

d1 = Date()
d1.day, d1.month, d1.year = 8, 3, 2012
print_date(d1)

d2 = increment_date(d1, 7)
print_date(d2)
```

### Exercise 16.8

1\. Use the *datetime* module to write a program that gets the current
date and prints the day of the week.

``` python
from datetime import date

def current_weekday():
    i = date.today()
    print i.strftime('%A')

current_weekday()
```

2\. Write a program that takes a birthday as input and prints the user's
age and the number of days, hours, minutes and seconds until their next
birthday.

``` python
# Python3 solution. Replace "input" by "raw_input" for Python2.
from datetime import datetime

def time_until_birthday():
    dob_input = input(('Please enter the date of your birth in '
                       'the format "mm/dd/yyyy": '))
    dob = datetime.strptime(dob_input, '%m/%d/%Y')
    now = datetime.now()
    if now > datetime(now.year, dob.month, dob.day):
        age = now.year - dob.year
        next_year = True
    else:
        age = now.year - dob.year - 1
        next_year = False
    time_to_birthday = datetime(now.year + next_year,
                                dob.month, dob.day) - now
    days = time_to_birthday.days
    hours, remainder = divmod(time_to_birthday.seconds, 3600)
    minutes, seconds = divmod(remainder, 60)
    print("\nYou are {} years old.".format(age))
    print(("You have {0} days, {1} hours, {2} minutes and {3} "
           "seconds left until your next birthday.").format(
               days, hours, minutes, seconds))

time_until_birthday()
```

## Chapter 17

### Exercise 17.8

2\.

``` python
from visual import scene, sphere

scene.range = (256, 256, 256)
scene.center = (128, 128, 128)

t = range(0, 256, 51)

for x in t:
    for y in t:
        for z in t:
            pos = x, y, z
            color = (x/255., y/255., z/255.)
            sphere(pos=pos, radius=10, color=color)
```

3\. Download <http://thinkpython.com/code/color_list.py> and use the
function *read_colors* to generate a list of the available colors on
your system, their names and RGB values. For each named color draw a
sphere in the position that corresponds to its RGB values.

``` python
# As there currently (2013-04-12) is no function read_colors in color_list.py
# I use a workaround and simply import the variable COLORS from color_list.py.
# I then use the function all_colors() on COLORS to get a list of the colors.

from color_list import COLORS
from visual import scene, sphere

def all_colors(colors_string=COLORS):
    """Extract a list of unique RGB-tuples from COLORS.
    The tuples look like (r, g, b), where r, g and b are each integers in
    [0, 255].
    """

    # split the string into lines and remove irrelevant lines
    lines = colors_string.split('\n')[2:-2]  

    # split the individual lines and remove the names
    numbers_only = [line.split()[:3] for line in lines]
    
    # turn strings into ints and rgb-lists into tuples
    rgb_tuples = [tuple([int(s) for s in lst]) for lst in numbers_only]

    # return a list of unique tuples
    return list(set(rgb_tuples))

def make_spheres(color_tuples=all_colors()):
    scene.range = (256, 256, 256)
    scene.center = (128, 128, 128)
    for (r, g, b) in color_tuples:
        sphere(pos=(r, g, b), radius=7, color=(r/255., g/255., b/255.))

if __name__ == '__main__':
    make_spheres()
```

## Chapter 3.5

### calculator

``` python
#recursion or recursive
print "\n   INDEX\n""\n C=1 for addition\n""\n  C=2 for substraction\n""\n  
C=3 for multiplication\n""\n    C=4 for division\n""\n  C=5 for to find modulus\n""\n   C=6 to find factorial\n"
C=input("Enter your choice here: ")
def add(x,y):
    c=x+y
    print x,"+",y,"=",c
def sub(x,y):
    c=x-y
    print x,"-",y,"=",c
def mul(x,y):
    c=x*y
    print x,"*",y,"=",c
def div(x,y):
    c=x/y
    print x,"/",y,"=",c
def mod(x,y):
    c=x%y
    print x,"%",y,"=",c
if C==6:
    def f(n):
        if n==1:
            print n
            return n
        else:
            print n,"*",
            return n*f(n-1)
    n=input("enter your no here: ")
    print f(n)
if C==1:
    a=input("Enter your first no here: ")
    b=input("Enter your second no here: ")
    add(a,b)
elif C==2:
    a=input("Enter your first no here: ")
    b=input("Enter your second no here: ")
    sub(a,b)
elif C==3:
    a=input("Enter your first no here: ")
    b=input("Enter your second no here: ")
    mul(a,b)
elif C==4:
    a=input("Enter your first no here: ")
    b=input("Enter your second no here: ")  
    div(a,b)
elif C==5:
    a=input("Enter your first no here: ")
    b=input("Enter your second no here: ")
    mod(a,b)
```

### palindrome

``` python
def first(word):
    return word[0]
def last(word):return word[-1]
def middle(word):
    return word[1:-1]
def palindrome(word):
    if first(word)==last(word):
        word = middle(word)
        n=len(word)
        if n<2:
            print "palindrome"
        else:       
            return palindrome(word)
    else:
        print "not palindrome"


word=raw_input("Enter the  string:")
palindrome(word)
```

### sum of all digits

``` python
def sum_of_n_numbers(number):
    if(number==0):
        return 0
    else:
        return number + sum_of_n_numbers(number-1)
num = raw_input("Enter a number:")
num=int(num)
sum = sum_of_n_numbers(num)
print sum
###another answer in case of while loops
def sum_of_Digits(number):
    sum=0
    while number>0:
        digit=number%10
        sum=sum+digit
        number=number/10
    return sum
num=raw_input("enter the number")
num=int(num)
sum_of_digits=sum_of_Digits(num)
print sum_of_digits 
```

### Exercise 18.5

``` python
class Card(object):
    
    suit_names = ['Clubs', 'Diamonds', 'Hearts', 'Spades']
    rank_names = [None, 'Ace', '2', '3', '4', '5', '6', '7', 
                    '8', '9', '10', 'Jack', 'Queen', 'King']
            
    def __init__(self, suit = 0, rank = 2):
        self.suit = suit
        self.rank = rank
    
    def __str__(self):
        return '%s of %s' % (Card.rank_names[self.rank], 
                            Card.suit_names[self.suit])
                            
    def __cmp__(self, other):
        c1 = (self.suit, self.rank)
        c2 = (other.suit, other.rank)
        return cmp(c1, c2)
        
    def is_valid(self):
        return self.rank > 0
        
class Deck(object):
    
    def __init__(self, label = 'Deck'):
        self.label = label
        self.cards = []
        for i in range(4):
            for k in range(1, 14):
                card = Card(i, k)
                self.cards.append(card)
                
    def __str__(self):
        res = []
        for card in self.cards:
            res.append(str(card))
        print self.label
        return '\n'.join(res)
        
        
    def deal_card(self):
        return self.cards.pop(0)
        
    def add_card(self, card):
        self.cards.append(card)
    
    def shuffle(self):
        import random
        random.shuffle(self.cards)
        
    def sort(self):
        self.cards.sort()
        
    def move_cards(self, other, num):
        for i in range(num):
            other.add_card(self.deal_card())
    
    def deal_hands(self, num_hands, num_cards):
        if num_hands*num_cards > 52:
            return 'Not enough cards.'
        
        l = []
        
        for i in range(1, num_hands + 1):
            hand_i = Hand('Hand %d' % i)
            self.move_cards(hand_i, num_cards)
            l.append(hand_i)
        
        return l

class Hand(Deck):
    
    def __init__(self, label = ''):
        self.cards = []
        self.label = label

# 18-6, 1-4:
class PokerHand(Hand):
    
    def suit_hist(self):
        self.suits = {}
        for card in self.cards:
            self.suits[card.suit] = self.suits.get(card.suit, 0) + 1
        return self.suits
        
    def rank_hist(self):
        self.ranks = {}
        for card in self.cards:
            self.ranks[card.rank] = self.ranks.get(card.rank, 0) + 1
        return self.ranks
    
    def P(self):
        self.rank_hist()
        for val in self.ranks.values():
            if val >= 2:
                return True
        return False
    
    def TP(self):
        self.rank_hist()
        count = 0
        for val in self.ranks.values():
            if val == 4:
                return True
            elif val >= 2 and val < 4:
                count += 1
        return count >= 2
        
    def TOAK(self):
        self.rank_hist()
        for val in self.ranks.values():
            if val >= 3:
                return True
        return False
    
    def STRseq(self):
        seq = []
        l = STRlist()
        self.rank_hist()
        h = self.ranks.keys()
        h.sort()
        if len(h) < 5:
            return []
        
        # Accounts for high Aces:
        if 1 in h:
            h.append(1)
        
        for i in range(5, len(h)+1):
            if h[i-5:i] in l:
                seq.append(h[i-5:i])
        return seq
    
    def STR(self):
        seq = self.STRseq()
        return seq != []

    def FL(self):
        self.suit_hist()
        for val in self.suits.values():
            if val >= 5:
                return True
        return False

    def FH(self):
        d = self.rank_hist()
        keys = d.keys()
        
        for key in keys:
            if d[key] >= 3:
                keys.remove(key)
                for key in keys:
                    if d[key] >= 2:
                        return True
        return False
        
    def FOAK(self):
        self.rank_hist()
        for val in self.ranks.values():
            if val >= 4:
                return True
        return False
        
    def SFL(self):
        seq = self.STRseq()
        if seq == []:
            return False
        for list in seq:
            list_suits = []
            for index in list:
                for card in self.cards:
                    if card.rank == index:
                        list_suits.append(card.suit)
            list_hist = histogram(list_suits)
            for key in list_hist.keys():
                if list_hist[key] >= 5:
                    return True
        return False
                
    def classify(self):
        self.scores = []
        hands = ['Pair', 'Two-Pair',
        'Three of a Kind', 'Straight',
        'Flush', 'Full House',
        'Four of a Kind', 'Straight Flush']
        if self.P():
            self.scores.append(1)
        if self.TP():
            self.scores.append(2)
        if self.TOAK():
            self.scores.append(3)
        if self.STR():
            self.scores.append(4)
        if self.FL():
            self.scores.append(5)
        if self.FH():
            self.scores.append(6)
        if self.FOAK():
            self.scores.append(7)
        if self.SFL():
            self.scores.append(8)
        if self.scores != []:
            return hands[max(self.scores)-1]
    
def STRlist():
    s = []
    for i in range(0,9):
        s.append(range(1,14)[i:i+5])
    s.append([10,11,12,13,1])   
    return s

def histogram(l):
    d = dict()
    for k in range(len(l)):
        d[l[k]] = 1 + d.get(l[k],0)
    return d

# 18-6, 5:
def p(config = '', trials = 10000, n = 1):
    """Estimates probability that the
    nth dealt hand will be config. A hand
    consists of seven cards."""
    
    successes = 0
    
    for i in range(1, trials + 1):
        deck = Deck('Deck %d' % i)
        deck.shuffle()
        
        box = Hand()
        deck.move_cards(box, (n-1)*7)
        
        hand = PokerHand('Poker Hand %d' % i)
        deck.move_cards(hand, 7)
        if hand.classify() == config:
            successes += 1
    
    return 1.0*successes/trials

#Iterate until first desired config.:
if __name__ == '__main__':
    
    c = 1
    
    while True:
        deck = Deck()
        deck.shuffle()
        hand = PokerHand('Poker Hand %d' % c)
        deck.move_cards(hand, 5)
        print hand
        print hand.SFL()
        if hand.SFL():
            print hand.STRseq()
            break
        print ''
        c += 1

Code by Victor Alvarez
```

## Appendix B

### Exercise B.1

Read the Wikipedia page on Big-Oh notation and answer the following
questions:

1\. *What is the order of growth of n³ + n²? What about 1000000n³ + n²?
What about n³ + 1000000n²?*

:   A: All are O(n³)

2\. *What is the order of growth of (n² + n) · (n + 1)? Before you start
multiplying, remember that you only need the leading term.*

:   A: O(n³)

3\. *If f is in O(g), for some unspecified function g, what can we say
about af + b, where a and b are constants?*

:   A: a and b are also O(g) since O-notation uses the leading
    coefficient. Constants are O(1), so they are irrelevant in this
    case.

4\. \'\'If f1 and f2 are in O(g), what can we say about f1 + f2?

:   A: Assuming the author means that g in this problem is separate from
    g the last problem, then O(g) remains unchanged.

5\. *If f1 is in O(g) and f2 is in O(h), what can we say about f1 + f2?*

:   A: f1 + f2 may or may not match the higher order of growth of either
    O(g) and O(h). If f1 or f2 are the leading coefficients, then f1 +
    f2 will have the same order of growth as the the largest order of
    growth of either O(g) or O(h). If that is not the case, then any
    information about order of growth of f1 + f2 is unknown to us. i.e.
    It doesn\'t matter that they are being added.

6\. *If f1 is in O(g) and f2 is O(h), what can we say about f1 · f2?*

:   A: This is different. If f1 and f2 are multiplied (and assuming they
    each contain an n in them) then O(f1 · f2) has to be O(n) or larger.
    It could be larger if f1 is n³, for example, but it must at least be
    O(n).

### Exercise B.3

Write a function called *bisection* that takes a sorted list and a
target value and returns the index of the value in the list, if it's
there, or *None* if it's not.

``` python
from bisect import bisect_left

def bisection(sorted_list, item):
    i = bisect_left(sorted_list, item)
    if i < len(sorted_list) and sorted_list[i] == item:
        return i
    else:
        return None

if __name__ == '__main__':
    a = [1, 2, 3]
    print(bisection(a, 2))  # expect 1
    b = [1, 3]
    print(bisection(b, 2))  # expect None
    c = [1, 2]
    print(bisection(c, 3))  # expect None
```

