In python I don't seem to be understanding the return function. Why use it when I could just print it?
def maximum(x, y):
if x > y:
print(x)
elif x == y:
print('The numbers are equal')
else:
print(y)
maximum(2, 3)
This code gives me 3
. But using return it does the same exact thing.
def maximum(x, y):
if x > y:
return x
elif x == y:
return 'The numbers are equal'
else:
return y
print(maximum(2, 3))
So what's the difference between the two? Sorry for the mega noob question!
The Point
return is not a function. It is a control flow construct (like if
else
constructs). It is what lets you "take data with you between function calls".
Break down
print
: gives the value to the user as an output string. print(3)
would give a string '3'
to the screen for the user to view. The program would lose the value.
return
: gives the value to the program. Callers of the function then have the actual data and data type (bool, int, etc...) return 3
would have the value 3 put in place of where the function was called.
Example Time
def ret():
return 3
def pri():
print(3)
4 + ret() # ret() is replaced with the number 3 when the function ret returns
# >>> 7
4 + pri() # pri() prints 3 and implicitly returns None which can't be added
# >>> 3
# >>> TypeError cannot add int and NoneType
What would you do if you need to save printed value? Have a look at good explanation in docs and cf.:
>>> def ret():
return 42
>>> def pri():
print(42)
>>> answer = pri()
42
>>> print(answer) # pri implicitly return None since it doesn't have return statement
None
>>> answer = ret()
>>> answer
42
It also is no different from return
statement in any other language.
For more complex calculations, you need to return intermediate values. For instance:
print minimum(3, maximum(4, 6))
You can't have maximum
printing its result in that case.
Remember that the interactive command line isn't the only place methods will be called from. Methods can also be called by other methods, and in that case print
isn't a usable way to pass data between them
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