In Python3.X, when passing methods into Map/Filter/Reduce, why is it done without '()'? Does this apply to all generators?
This is probably a simple question but I can't find a clear answer in docs. I'm hoping to understand the reasons rather than just "memorizing" syntax.
e.g.
map(str.upper, ['a', 'b', 'c']) #this works
vs
map(str.upper(), ['a', 'b', 'c']) #this gives an error
This is confusing at first, especially when you come from other programming languages. In Python the functions are objects and you can pass them along without invoking them. Check below example:
def func(): # function definition
print("func was invoked")
a = func # assign func object (without invoking it)
print(a, type(a))
a() # invoking the function
map will use this function object to invoke the function for each item in the iterable.