def str_startswith(arr, pat, na=np.nan):
f = lambda x: x.startswith(pat)<EOL>return _na_map(f, arr, na, dtype=bool)<EOL>
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