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Question

I am slightly confused by map in python. The function for map accepts 2 parameters: `map(function, variables).

Why is the code below able to take in multiply and add as variables but the second code isn't able to? In a usual case, multiply should be passed in in as a function, check out range.

def multiply(x):
    return x * x

def add(x):
    return x + x

funcs = [multiply, add]

for i in range (1, 5):
    value = list(map(lambda x: x(i), funcs))
    print(value)

This is the second code:

def multiply(x):
    return x * x

def add(x):
    return x + x

funcs = (add, multiply)
multi_func = (multiply)

for i in range (1, 5):
    value = list(map(lambda x: x(i), multi_func))
    print(value)

Is it possible to make use of 1 function and still use for in range?

Using range:

map(multiply, range(1, 5))

Answer 1

map applies its first argument, which is a function, to each element of the iterable which is the second argument. The function is applied lazily. That means it's done only when you iterate over the map object, eg, when you create a list of of it.

Let's take a look at your first code. funcs = [multiply, add] creates a list, which is iterable, of two elements. Both elements are functions. This is normal in Python, because functions are just regular objects, and can be passed around, assigned, have attributes, etc. The loop

for i in range (1, 5):
    value = list(map(lambda x: x(i), funcs))
    print(value)

Repeats form 1 to 4. At each iteration it maps lambda x: x(i) to the functions in funcs . When i = 1 , the map ends up doing multiply(1), add(1) . When i = 2 , it's multiply(2), add(2) , and so on.

The second code doesn't work because of a typo. (x) is just x , but (x,) is a one-element tuple whose first element is x . map requires the second argument to be iterable, so passing in a function won't do. If you want to map to a single function, you need to supply an iterable with one element: multi_func = (multiply,) .

Once corrected, the second version will print multiply(1) when i = 1 , multiply(2) when i = 2 , etc.

Something like list(map(multiply, range(1, 5))) will in fact be an easier way to write the second version. You can also do something similar with the first code, using zip :

zip(map(func, range(1, 5)) for func in funcs)