How to better understand Pure and impure Function in Python.

Question

How to deeply understand about Python functional programming.

Answer 1

# Create a global variable `A`.
A = 5

def impure_sum(b):
# Adds two numbers, but uses the
# global `A` variable.
return b + A

def pure_sum(a, b):
# Adds two numbers, using
# ONLY the local function inputs.
return a + b

print(impure_sum(6))
#11

print(pure_sum(4, 6))
#10

Thank you...Sooo much 😊

Answer 2

Can you please little bit more explain about impure function, with sample program.??

Answer 3

https://www.sololearn.com/discuss/1569927/?ref=app
https://www.sololearn.com/discuss/1714494/?ref=app
https://www.sololearn.com/discuss/1483564/?ref=app

Answer 4

Pure function: does nothing to the outer program, just returns a value.

def pure(x):
return x * 3

Impure functions, however do stuff, too.
So, a lot of people use impure functions for not a good reason:

def impure(x):
print(x * 3)

This is not good, because sometimes you want to use the function in equations, for example:

i = pure(8) + 1

But you cannot do that with impure functions without disturbing the program.

Answer 5

Because it outputs stuff on the screen. So you cannot quietly run the function 100 times without anyone noticing.

So, if you do
triples = [times3(x) for x in range(100)]

Then you might notice what I mean

Answer 6

Impure functions somehow change the state of the program. So,

def times3(x):
print("Counting the three times", x, "...")
return x * 3

This is also an impure function (a very annoying one, if I must say). But impure functions don't necessarily have to output something:

timesCalled = 0

def times3(x):
timesCalled += 1
return x * 3

This is also impure.

I'm not sure if I can explain it more to you, it's pretty simple

Answer 7

Well simply pure functions are functions, that only uses it's parameters to receive data from outside.

#Pure:
def f(x):
return x + 7

Inpure:
a = 15
def f(x):
return x + a
#Uses variable a, which was defined outside and not received as argument.