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Practical tips for using map()

When using map() you sometimes can be fooled by Pythons lazy evaluation. Many functions returning complex or iterable data don’t do this directly but return a generator object, which when iterated over, yields the result values.

But sometimes you will need the result set at once. For example when map()ing a list one would sometimes coerce Python to return the whole resulting list. This can be done by applying the list() function to the generator like this:

l1=map(lambda x: x+1, l)
<map object at 0x10f4536d8>
l1=map(lambda x: x+1, l) 
[2, 3, 4]


In line 5 I have to recreate the map object since print() seems to empty it.

When applying a standard function with map() it’s needed to qualify the module path on call:

l=["Hello  ", "  World"]
l1=map(strip, l)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
NameError: name 'strip' is not defined

In this case it’s the str module:

l1=map(str.strip, l)
['Hello', 'World']


Thats all for now. Have fun.