# Python Language Map Function Mapping values of different iterables

## Example

For example calculating the average of each `i`-th element of multiple iterables:

``````def average(*args):
return float(sum(args)) / len(args)  # cast to float - only mandatory for python 2.x

measurement1 = [100, 111, 99, 97]
measurement2 = [102, 117, 91, 102]
measurement3 = [104, 102, 95, 101]

list(map(average, measurement1, measurement2, measurement3))
# Out: [102.0, 110.0, 95.0, 100.0]
``````

There are different requirements if more than one iterable is passed to `map` depending on the version of python:

• The function must take as many parameters as there are iterables:

``````def median_of_three(a, b, c):
return sorted((a, b, c))

list(map(median_of_three, measurement1, measurement2))
``````

TypeError: median_of_three() missing 1 required positional argument: 'c'

``````list(map(median_of_three, measurement1, measurement2, measurement3, measurement3))
``````

TypeError: median_of_three() takes 3 positional arguments but 4 were given

Python 2.x2.0.1
• `map`: The mapping iterates as long as one iterable is still not fully consumed but assumes `None` from the fully consumed iterables:

``````import operator

measurement1 = [100, 111, 99, 97]
measurement2 = [102, 117]

# Calculate difference between elements
list(map(operator.sub, measurement1, measurement2))
``````

TypeError: unsupported operand type(s) for -: 'int' and 'NoneType'

• `itertools.imap` and `future_builtins.map`: The mapping stops as soon as one iterable stops:

``````import operator
from itertools import imap

measurement1 = [100, 111, 99, 97]
measurement2 = [102, 117]

# Calculate difference between elements
list(imap(operator.sub, measurement1, measurement2))
# Out: [-2, -6]
list(imap(operator.sub, measurement2, measurement1))
# Out: [2, 6]
``````
Python 3.x3.0.0
• The mapping stops as soon as one iterable stops:

``````import operator

measurement1 = [100, 111, 99, 97]
measurement2 = [102, 117]

# Calculate difference between elements
list(map(operator.sub, measurement1, measurement2))
# Out: [-2, -6]
list(map(operator.sub, measurement2, measurement1))
# Out: [2, 6]
``````