DOC: f2py: Add a docstring for getarrlen

The API of this function is awful, and I still have no idea what it does.
Maybe someone reading the docstring will be able to work it out.

1 files changed, 31 insertions, 0 deletions

diff --git a/numpy/f2py/crackfortran.py b/numpy/f2py/crackfortran.py
index 1fe2ca037..2e95e4596 100755
--- a/numpy/f2py/crackfortran.py
+++ b/numpy/f2py/crackfortran.py
@@ -2187,6 +2187,37 @@ _varname_match = re.compile(r'\A[a-z]\w*\Z').match
 
 
 def getarrlen(dl, args, star='*'):
+    """
+    Parameters
+    ----------
+    dl : sequence of two str objects
+        dimensions of the array
+    args : Iterable[str]
+        symbols used in the expression
+    star : Any
+        unused
+
+    Returns
+    -------
+    expr : str
+        Some numeric expression as a string
+    arg : Optional[str]
+        If understood, the argument from `args` present in `expr`
+    expr2 : Optional[str]
+        If understood, an expression fragment that should be used as
+        ``"(%s%s".format(something, expr2)``.
+
+    Examples
+    --------
+    >>> getarrlen(['10*x + 20', '40*x'], {'x'})
+    ('30 * x - 19', 'x', '+19)/(30)')
+    >>> getarrlen(['1', '10*x + 20'], {'x'})
+    ('10 * x + 20', 'x', '-20)/(10)')
+    >>> getarrlen(['10*x + 20', '1'], {'x'})
+    ('-10 * x - 18', 'x', '+18)/(-10)')
+    >>> getarrlen(['20', '1'], {'x'})
+    ('-18', None, None)
+    """
     edl = []
     try:
         edl.append(myeval(dl[0], {}, {}))