<p>Given a string <code>s</code> representing a valid expression, implement a basic calculator to evaluate it, and return <em>the result of the evaluation</em>.</p>

<p><strong>Note:</strong> You are <strong>not</strong> allowed to use any built-in function which evaluates strings as mathematical expressions, such as <code>eval()</code>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;1 + 1&quot;
<strong>Output:</strong> 2
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> s = &quot; 2-1 + 2 &quot;
<strong>Output:</strong> 3
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;(1+(4+5+2)-3)+(6+8)&quot;
<strong>Output:</strong> 23
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= s.length &lt;= 3 * 10<sup>5</sup></code></li>
	<li><code>s</code> consists of digits, <code>&#39;+&#39;</code>, <code>&#39;-&#39;</code>, <code>&#39;(&#39;</code>, <code>&#39;)&#39;</code>, and <code>&#39; &#39;</code>.</li>
	<li><code>s</code> represents a valid expression.</li>
	<li><code>&#39;+&#39;</code> is <strong>not</strong> used as a unary operation (i.e., <code>&quot;+1&quot;</code> and <code>&quot;+(2 + 3)&quot;</code> is invalid).</li>
	<li><code>&#39;-&#39;</code> could be used as a unary operation (i.e., <code>&quot;-1&quot;</code> and <code>&quot;-(2 + 3)&quot;</code> is valid).</li>
	<li>There will be no two consecutive operators in the input.</li>
	<li>Every number and running calculation will fit in a signed 32-bit integer.</li>
</ul>

nums = set(map(chr, range(ord('0'), ord('9') + 1)))
def calc_func(c: str):
    if c == '+':
        return lambda a, b: a + b
    elif c == '-':
        return lambda a, b: a - b
    else:
        raise Exception("bozo")

def get_num(s: str) -> (int, int):
    # takewhile isnum s
    i = 0
    c = ''
    while i < len(s) and s[i] in nums:
        c += s[i]
        i += 1
    return int(c), len(c)
    
class Solution:
    def calculate(self, s: str) -> int:
        print(nums)
        return self._calculate(''.join([c for c in s if c != ' ']))
    def _calculate(self, s: str) -> int:
        i = 0
        stack = [(0, 1)]
        while i < len(s):
            if s[i] == '-':
                if s[i+1] in nums:
                    # negative number
                    n, num_taken = get_num(s[i+1:])
                    stack[-1] = stack[-1][0] - n, stack[-1][1]
                    i += num_taken + 1
                elif s[i+1] == '(':
                    stack.append((0, -1))
                    i += 2
                else:
                    raise Exception("formatting error")
            elif s[i] in nums:
                n, num_taken = get_num(s[i:])
                stack[-1] = stack[-1][0] + n, stack[-1][1]
                i += num_taken
            elif s[i] == '(':
                stack.append((0, 1))
                i += 1
            elif s[i] == ')':
                v = stack.pop(-1)
                if len(stack) == 0:
                    return v[0] * v[1]
                else:
                    stack[-1] = stack[-1][0] + v[0] * v[1], stack[-1][1]
                i += 1
            else:
                i += 1
        if len(stack) > 1:
            raise Exception("bruh")
        return stack[0][0] * stack[0][1]

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