Error Correction

errorCorrection.py

# This works
def printHelloWorld():
  print('hello word')

def returnPrintHelloWorld():
  return print('hello world') # output: syntax error

"""

To answer the original question: Why do you use a return statement on the return 5
function but not on the printHelloWorld() function?

The printHelloWorld() function is calling another function. It happens to be that the
inner function it is calling - print() - is a built in Python function that 
independently performs an "action"

Whereas the other function is literally returning a variable. The "action" is 
returning a value

  File "/Users/Home/Documents/Programming Work/LaunchCode/Lectures/Lecture1/test.py", 
  line 6
    return print('hello world') # output: fails with syntax error
               ^
SyntaxError: invalid syntax

This errors because the print() function does not return a value that 
the outer function can then return.
print() is a built in Python function and does not return any value
https://docs.python.org/3/library/functions.html#print


See this example below to understand that functions can return other functions
but only if the inner function returns an actual value

We have a function called returnAnIntValue() which returns the integer 5
Because it returns a value it can be returned by another function

The reason this works is because functions EVALUATE from the inside out

This might be confusing but is actual intuitive. You are calling the functions
from the outside in but then returning the values from the inside out as they
are evaluated so the outermost function can make use of the innermost value

Here are the steps occuring during the call on line 25 print(returnAFunction1())

Function Call Steps ("forward, out to in order":
1) call print()
  argument: returnAFunction1()
2) call returnAFunction1()
  return returnAnIntValue()
3) call returnAnIntValue()
  return 5

Function Evaluation Steps ("reverse, in to out order"):
1) evaluate innermost function call: returnAnIntValue()
  returns 5
2) evaluate second innermost function call: returnAFunction1()
  returns returnAnIntValue() --( evaluated in step 1) )--> returns a 5
3) evaluate outermost function call: print()
  print(returnAFunction1()) --( evaluated through steps 1) and 2) )--> print(5)

The same can be shown for the print call on line 53, this time evaluating to a string

"""

def returnAnIntValue():
  return 5

def returnAFunction1():
  return returnAnIntValue()

print(returnAFunction1()) # output: 5

def returnAStringValue():
  return 'a string'

def returnAFunction2():
  return returnAStringValue()

print(returnAFunction2()) # output: a string