Python: calling method in the map function
list-comprehension, map-function, methods, python
Solution
You'd use `operator.methodcaller()`:
from operator import methodcaller
map(methodcaller('function'), list1)
`methodcaller()` accepts additional arguments that are then passed into the called method; `methodcaller('foo', 'bar', spam='eggs')(object)` is the equivalent of `object.foo('bar', spam='eggs')`.
If all objects in `list1` are the same type or subclasses of that type, and the method you want to call doesn't take any arguments, you can pass in the unbound method to `map` as the function to call. For example, to lowercase all strings in a list, you can use:
map(str.lower, list_of_strings)
where `str.lower` is the unbound method on the `str` type.
Note that a list comprehension is not really the equivalent of a `map()` here. `map()` can only do one loop, entirely in C. `map()` will `zip()` multiple iterable arguments, and `map()` in Python 3 is itself an iterator.
A list comprehension on the other hand can do multiple (nested) loops and add in filtering, and the left-hand expression can be any valid Python expression including nested list comprehensions.
Problem
`map()` and list comprehension are roughly equivalent: ``` map(function, list1) [function(i) for i in list1] ``` What if the function we want to use is a method? ``` [i.function() for i in list1] map(.function, list1) # error! map(run_method(function), list1) # error! ``` How could I perform this kind of manipulation with `map`?