parameters: (arr, pat, na=np.nan)
return_statement: return _na_map(f, arr, na, dtype=bool)
docstring: Test if the start of each string element matches a pattern.
  
      Equivalent to :meth:`str.startswith`.
  
      Parameters
      ----------
      pat : str
          Character sequence. Regular expressions are not accepted.
      na : object, default NaN
          Object shown if element tested is not a string.
  
      Returns
      -------
      Series or Index of bool
          A Series of booleans indicating whether the given pattern matches
          the start of each string element.
  
      See Also
      --------
      str.startswith : Python standard library string method.
      Series.str.endswith : Same as startswith, but tests the end of string.
      Series.str.contains : Tests if string element contains a pattern.
  
      Examples
      --------
      >>> s = pd.Series(['bat', 'Bear', 'cat', np.nan])
      >>> s
      0     bat
      1    Bear
      2     cat
      3     NaN
      dtype: object
  
      >>> s.str.startswith('b')
      0     True
      1    False
      2    False
      3      NaN
      dtype: object
  
      Specifying `na` to be `False` instead of `NaN`.
  
      >>> s.str.startswith('b', na=False)
      0     True
      1    False
      2    False
      3    False
      dtype: bool
docstring_summary: Test if the start of each string element matches a pattern.
docstring_tokens: Test if the start of each string element matches a pattern .
function: def str_startswith(arr, pat, na=np.nan):
      """
      Test if the start of each string element matches a pattern.
  
      Equivalent to :meth:`str.startswith`.
  
      Parameters
      ----------
      pat : str
          Character sequence. Regular expressions are not accepted.
      na : object, default NaN
          Object shown if element tested is not a string.
  
      Returns
      -------
      Series or Index of bool
          A Series of booleans indicating whether the given pattern matches
          the start of each string element.
  
      See Also
      --------
      str.startswith : Python standard library string method.
      Series.str.endswith : Same as startswith, but tests the end of string.
      Series.str.contains : Tests if string element contains a pattern.
  
      Examples
      --------
      >>> s = pd.Series(['bat', 'Bear', 'cat', np.nan])
      >>> s
      0     bat
      1    Bear
      2     cat
      3     NaN
      dtype: object
  
      >>> s.str.startswith('b')
      0     True
      1    False
      2    False
      3      NaN
      dtype: object
  
      Specifying `na` to be `False` instead of `NaN`.
  
      >>> s.str.startswith('b', na=False)
      0     True
      1    False
      2    False
      3    False
      dtype: bool
      """
      f = lambda x: x.startswith(pat)
      return _na_map(f, arr, na, dtype=bool)
function_tokens: def str_startswith ( arr , pat , na = np . nan ) : f = lambda x : x . startswith ( pat ) return _na_map ( f , arr , na , dtype = bool )