Function print

Python has a built-in function named print that displays messages to the user. For example, the following function call displays the string "hello":

>>> print("hello")
hello

The print function may also be called with a mathematical expression for an argument. Python evaluates the mathematical expression first and then displays the resulting value to the user. For example:

>>> print(3 + 7 - 3)
7

Finally, print can take in more than one argument. Each pair of arguments is separated by a comma and a space is inserted between them when they are displayed. For example:

>>> print("hello", "there")
hello there

return vs. print

return expression

• What is passed back to the caller?
  That memory address is passed back to the caller.
• What is displayed?
  Nothing!

An example of return:

>>> def square_return(num):
    return num ** 2
>>> answer_return = square_return(4)  
>>> answer_return 
16      

The general form of a print function call:

print(arguments)

• What is passed back to the caller?
  Nothing!
• What is displayed?
  The values at those memory address(es) are displayed on the screen.

An example of print:

>>> def square_print(num):
    print("The square of num is", num ** 2)
>>> answer_print = square_print(4)
The square num is 16
>>> answer_print
>>>

Function input

The function input is a built-in function that prompts the user to enter some input. The program waits for the user to enter the input, before executing the subsequent instructions. The value returned from this function is always a string. For example:

>>> input("What is your name? ")
What is your name? Jen
'Jen'
>>> name = input("What is your name? ")
What is your name? Jen
>>> name
'Jen'
>>> location = input("What is your location? ")
What is your location? Toronto
>>> location
'Toronto'
>>> print(name, "lives in", location)
Jen lives in Toronto
>>> num_coffee = input("How many cups of coffee? ")
How many cups of coffee? 2
>>> num_coffee
'2'

Operations on strings

Triple-quoted strings

We have used single- and double- quotes to represent strings. The third string format uses triple-quotes and a triple-quoted string can span multiple lines. For example:

>>> print(''' How
are
you?''')
How
are 
you?

Escape Sequences

Python has a special character called an escape character: \. When the escape character is used in a string, the character following the escape character is treated differently from normal. The escape character together with the character that follows it is an escape sequence. The table below contains some of Python's commonly used escape sequences.

3   4       5

print('\\')

\

print('don\'t')

don't

print("He says, \"hi\".")

He says, "hi".