CODEWITHSUNDEEP
python
Skitzafreak
Skitzafreak

Reputation: 1917

Understanding Python Maps()

So I am trying to figure out how Python's map() function works as a way to speed up my program a little bit. From my basic understanding it looks like you can use map() to replace certain instances where you'd use a for loop. What I'm curious about is can you change something like:

loopNum = 25
for i in range (loopNum):
    self.doSomething()

To:

loopNum = 25
map(self.doSomething(), range(loopNum))

Additionally, in the above example, would I be able to forego that loopNum variable, and in the map just have map(something, 25)?

Upvotes: 0

Views: 86

Answers (3)

GIZ
GIZ

Reputation: 4643

map is roughly the equivalent of this for loop:

# my_map(func, iter1, iterN...) 
def my_map(func, *iteables)
    for x, y,... in zip(iter1, iter2,iterN...): 
        yield func(x,y,...)

What you're doing in your code is just like this:

my_map(self.doSomething(), range(loopNum))

self.dSomething() must return a function or a callable object or this obviously doesn't work. This is because, whatever object you pass into the func argument of my_map function will be called then in addition to passing the right number of arguments to func, func must be a callable object as well :-)

*You must iterate over the iterable returned by map to obtain the results, otherwise, you would just get an iterable object without tangible work.

Upvotes: 1

JohanL
JohanL

Reputation: 6891

I want to add to this question that map() is virtually never the right tool in Python. Our BDFL himself, wanted to remove it from Python 3, together with lambdas and, most forcefully reduce.

In almost all cases where you feel tempted to use map() take a step back and try to rewrite your code using list comprehension instead. For your current example, that would be:

my_list = [self.doSomething() for i in range(loopNum)]

or 

my_generator = (self.doSomething() for i in range(loopNum))

to make it a generator instead.

But for this to make any sense at all, self.doSomething() should probably take the variable i as an input. After all you are trying to map the values in your range to something else.

Upvotes: 0

ForceBru
ForceBru

Reputation: 44886

No, you can't as map(function, iterable) applies function to each element of the iterable. If you simply want to execute some functionn times, just use a loop.

Note that iterable must be (surprise!) an iterable, not a number.

Upvotes: 4

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