DOC: update the pandas.Series.str.startswith docstring (#20458)

* DOC: update the pandas.Series.str.startswith docstring

* DOC: update the pandas.Series.str.startswith docstring

* DOC: update the pandas.Series.str.startswith docstring 2

* DOC: update the pandas.Series.str.startswith docstring 3

* DOC: update the pandas.Series.str.startswith docstring 4

Author: dcreekp

pandas/core/strings.py

@@ -328,19 +328,54 @@ def str_contains(arr, pat, case=True, flags=0, na=np.nan, regex=True):
 
 def str_startswith(arr, pat, na=np.nan):
     """
-    Return boolean Series/``array`` indicating whether each string in the
-    Series/Index starts with passed pattern. Equivalent to
-    :meth:`str.startswith`.
+    Test if the start of each string element matches a pattern.
+
+    Equivalent to :meth:`str.startswith`.
 
     Parameters
     ----------
-    pat : string
-        Character sequence
-    na : bool, default NaN
+    pat : str
+        Character sequence. Regular expressions are not accepted.
+    na : object, default NaN
+        Object shown if element tested is not a string.
 
     Returns
     -------
-    startswith : Series/array of boolean values
+    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)