CODEWITHSUNDEEP
pythondictionaryfunctional-programming
Ankit Solanki
Ankit Solanki

Reputation: 680

Python: Map calling a function not working

Map not calling the function being passed.

class a:
    def getDateTimeStat(self,datetimeObj):
        print("Hello")

if __name__ == "__main__":
    obj = a()
    print("prog started")
    data = [1,2,3,4,5]
    b = list(map(obj.getDateTimeStat,data))

Expected op on a new line: Hello Hello Hello Hello Hello

Any help will be appreciated....

Upvotes: 12

Views: 15691

Answers (3)

Tim Peters
Tim Peters

Reputation: 70735

You're using Python 3, right? map() returns an iterator in Python 3, not a list. So use any of the ways to force an iterator to produce its results; for example,

b = list(map(obj.getDateTimeStat,data))

Later

Here I'm running the exact code currently in your question:

class a:
    def getDateTimeStat(self,datetimeObj):
        print("Hello")

if __name__ == "__main__":
    obj = a()
    print("prog started")
    data = [1,2,3,4,5]
    b = list(map(obj.getDateTimeStat,data))

And here's the output:

$ python -V
Python 3.3.2

$ python yyy.py
prog started
Hello
Hello
Hello
Hello
Hello

Show exactly what happens - as I did for you.

Upvotes: 2

Blender
Blender

Reputation: 298532

Python 3's map function is lazy, unlike Python 2's map.

You have to consume it somehow:

for result in map(...):
    pass

Non-lazy evaluation version of map in Python3? highlights a few more elegant solutions.

Upvotes: 7

Pandu
Pandu

Reputation: 1686

In Python 3, map values are evaluated lazily. That is, each value is only computed when it's needed. You'll find that regardless of what function you use, it won't get called until you ask for the value of that item in the mapped result, whether by using next() or some other way.

To get what you want, you can do this:

>>> b = map(obj.getDateTimeStat,data)
>>> next(b)
Hello
>>> next(b)
Hello
>>> next(b)
Hello
>>> next(b)
Hello
>>> next(b)
Hello
>>> next(b)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
StopIteration

Or this:

>>> b = list(map(obj.getDateTimeStat,data))
Hello
Hello
Hello
Hello
Hello

Or a variety of other things.

Upvotes: 37

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