Question

is it possible to write a wrapper function for methods?

>>> lowtide = [ 'oh', 'i', 'do', 'like', 'to', 'be', 'beside', 'the', 'seaside' ]

>>> [ x.capitalize() for x in lowtide ]
['Oh', 'I', 'Do', 'Like', 'To', 'Be', 'Beside', 'The', 'Seaside']

>>> list(map(lambda x: x.capitalize(), lowtide))
['Oh', 'I', 'Do', 'Like', 'To', 'Be', 'Beside', 'The', 'Seaside']


>>> def mef(m):
...     def _mef(m,x):
...         return x.m()
...     return partial(_mef, m)
... 
>>> list(map(mef(capitalize), lowtide))

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'capitalize' is not defined

Answer 1

Although you can use str.capitalize and unicode.capitalize, these can fail if you assume a certain type… The safest method is to just use:

from operator import methodcaller
capitalize = methodcaller('capitalize')

Which guarantees the correct method is used for the object, and also allows duck typing to be done successfully.

excerpt from a post from me to Google Groups/comp.lang.python 23 Aug 2010

Using methodcaller allows you to ‘preserve’ Python’s duck-typing as
well as any over-ridden methods in subclasses. In your example, this
is probably overkill as you’re only dealing with one class

Another (convoluted) example:

class mystr(str):
    def lower(self):
        return self.upper()

>>> s = mystr('abc')
>>> s.lower()
'ABC'

>>> lower = methodcaller('lower')
>>> lower(s)
'ABC'

>>> str.lower(s)
'abc'

^^^ Most likely incorrect

It also adds a further bit of flexibility (which can be emulated with
functools.partial admittedly):

split_tab = methodcaller('split', '\t')
split_comma = methodcaller('split', ',')