webinar-functions-2020-06-12.py

# webinar functions and methods in Python

# You'll start getting to know functions in Ch 7

# functions should be modular and reusable
# we define a function once and call it as many times as needed

# defining a function
def myFunction(parameter1, parameter2):
    # indented block for my function
    # print() a value..
    print(parameter1, parameter2)
    # or return someValue instead, we'll do that next time

myFunction("Hey", "There")
myFunction("Goodbye", "... now")
print(myFunction("Hey", "There")) # this will also output "None", b/c I printed a call to a function with no return

# function definition, Gallant
def squareThis(num):
    return num * num # RETURN means the function calls evaluate to and give back this new value

# ... but you don't SEE a returned value, unless you print() the call itself
print(squareThis(5)) # 25
# because we returned this time, we can use calls to this function in assignment statements
x = squareThis(6) # 36... but not until I print it
print(x)
x = 10 + squareThis(7) # 59
print(x)

# Note that if the function prints instead of returning, you can't use that for assignment or other expressions
# Related: printing a call to a function with no return statement will show NONE in output

# bad function from Goofus
def squareSomething(num):
    num = 5 # don't do this!
    return num * num

print("Gallant vs Goofus: ")
print(squareThis(8)) # 64
print(squareSomething(8)) # 64? Nope it's value is 25
print(squareThis(3)) # 9
print(squareSomething(3)) # 9? Nope it's value is still 25

# Don't overwrite your parameters like Goofus!

# Pay close attention on the exam to whether a question asks you
# to RETURN or to PRINT() a value from the function.

# If you see "None" in your output, you called print() when you should have returned!

# You'll be getting to know various methods of common data types in Ch 8 and beyond
# METHODS of a data type or "class" are just functions that belong to that type
myList = [1, 2, 3, 4, 5, 3]
# nameOfObject.method()
count = myList.count(3) # this .count() is a list method, other types don't have it!
print(count) # 2
print(myList.count(3)) # or I can print the call, because .count() returns something
# help(list) # the built-in function help() will show me a help doc on a data type, including its methods