Question: How to use kwarg arguments when evaluating a function using map functionality

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How to use kwarg arguments when evaluating a function using map functionality

Answers 1
Added at 2017-01-05 16:01
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Below is an example of a test method which is evaluated using a for loop and a kwarg argument.

def test(first_arg='_', second_arg='_'):
    return 'first_arg: %s\t second_arg: %s' % (first_arg, second_arg)

strings = ['a', 'b', 'c', 'd', 'e']

for s in strings:
    print(test(second_arg=s))

How can the same result be achieved using map functionality? That is, how can a kwarg be passed into the map function?:

for i in map(test, strings):
    print(i)

The order of the arguments in the test function cannot be changed and passing all arguments is not acceptable. That is, the below map-equivalent solutions are not desired:

# Passing two arguments is not a desired solution.
for s in strings:
    print(test(first_arg='_', second_arg=s))

OR

# Editing the order of kwargs is also not possible.
def test(second_arg='_', first_arg='_'):
    return 'first_arg: %s\t second_arg: %s' % (first_arg, second_arg)

for s in strings:
    print(test(s))
Answers
nr: #1 dodano: 2017-01-05 16:01

You can use lambda to create a new function that calls test() with second_arg=x using its only argument x :

for i in map(lambda x: test(second_arg=x),  strings):
    print(i)

the output:

first_arg: _     second_arg: a
first_arg: _     second_arg: b
first_arg: _     second_arg: c
first_arg: _     second_arg: d
first_arg: _     second_arg: e

is the same as for this:

for s in strings:
    print(test(second_arg=s))

Output:

first_arg: _     second_arg: a
first_arg: _     second_arg: b
first_arg: _     second_arg: c
first_arg: _     second_arg: d
first_arg: _     second_arg: e

Alternatively, you can define a helper function. This is equivalent to the solutions with lambda above:

def call_with_second(x):
    return test(second_arg=x)

for i in map(call_with_second,  strings):
    print(i)

Output:

first_arg: _     second_arg: a
first_arg: _     second_arg: b
first_arg: _     second_arg: c
first_arg: _     second_arg: d
first_arg: _     second_arg: e
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