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I have a list of strings that I need to sanitize. I have a method for sanitizing them, so I could just do:
new_list = map(Sanitize, old_list)
but I don't need to keep the old list around. This got me wondering if there's an in-place equivalent to map. Easy enough to write a for loop for it (or a custom in-place map method), but is there anything built in?
574
Using Generator Expressions map() returns a map object, which is an iterator that yields items on demand. So, the natural replacement for map() is a generator expression because generator expressions return generator objects, which are also iterators that yield items on demand.
Map in Python is a function that works as an iterator to return a result after applying a function to every item of an iterable (tuple, lists, etc.). It is used when you want to apply a single transformation function to all the iterable elements. The iterable and function are passed as arguments to the map in Python.
In Python, dictionaries (or “dicts”, for short) are a central data structure: Dicts store an arbitrary number of objects, each identified by a unique dictionary key. Dictionaries are often also called maps, hashmaps, lookup tables, or associative arrays.
Comparing performance , map() wins! map() works way faster than for loop. Considering the same code above when run in this ide.
The answer is simply: no.
Questions of the form "does XXX exist" never tend to get answered directly when the answer is no, so I figured I'd put it out there.
Most itertools helpers and builtins operate on generic iterators. map, filter, list comprehensions, for--they all work on iterators, not modifying the original container (if any).
Why aren't there any mutating functions in this category? Because there's no generic, universal way to assign values to containers with respect to their keys and values. For example, basic dict iterators (for x in {}) iterate over the keys, and assigning to a dict uses the result of the dict as the parameter to []. Lists, on the other hand, iterate over the values, and assignment uses the implicit index. The underlying consistency isn't there to provide generic functions like this, so there's nothing like this in itertools or in the builtins.
They could provide it as a methods of list and dict, but presently they don't. You'll just need to roll your own.
123
You have to loop:
for i in range(len(old_list)):
old_list[i] = Sanitize(old_list[i])
There's nothing built-in.
As suggested in the comments: a function as desired by the OP:
def map_in_place(fn, l):
for i in range(len(l)):
l[i] = fn(l[i])
map_in_place(Sanitize, old_list)
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