Operators and the print() Function

What Will We Learn?

• Operators (*, /, -, +, %)
• The print() function (the function that lets us write text to the screen)

Operators

Mathematical Operators

Mathematical operators let us perform mathematical operations in Python. Let’s do a few examples to understand this topic better.

>>> 4 + 5 # addition
9
>>> 4 - 5 # subtraction
-1
>>> 4 * 5 # multiplication
20
>>> "Hakan "+"celik" # we can add two strings
'Hakan celik'
>>> "-"*5 # we can multiply a string
----- # there will be 5 dashes
>>> 4 / 5 # division
0.8
>>> 4 ** 5 # exponentiation
1024
>>> 4 % 5 # mod — gives the remainder of dividing 4 by 5
4
>>> 4 // 5 # floor division — gives the quotient of dividing 4 by 5
0

Comparison Operators

Comparison operators let us perform a comparison between operands — 3 is greater than 2, 3 equals 3, and so on.

Below is a small number-guessing script — you can understand it by examining it.

num = 99 # I assigned a number
get_num = input("Enter a number >> ") # I got a number from the user
if get_num > num: # if the user's number is greater than mine
    print("Go lower") # I printed "Go lower"
elif get_num < num: # if the user's number is lower
    print("Go higher") # I printed "Go higher"
else: # no condition was met — i.e., they are equal
    print("Correct!") # I printed "Correct!"

Boolean Operators

We all know that computers are built on 0 and 1 — binary: open, closed, present, absent, true, false. Computer science is built on these two values. These bool values are True and False.

For example:

>>> 1 == 1 # this is not assignment — it's the equality sign from mathematics, a comparison operator
True
>>> 1 == 2 # 1 is not equal to 2
False

We said that computer science is built on 0 and 1, and that these are True and False. From this we can conclude that everything in a computer has a bool value.

In a computer, everything except 0 and the empty character has a value of True. Let’s demonstrate this with a function called bool():

>>> bool(0)
False
>>> bool(-1)
True
>>> bool("")
False
>>> bool("hello")
True
>>> bool(1)
True
>>> bool("0") # this is a character — it's the string "0" — so it returns True
True
>>> 3 < 4
True
>>> "hakan" == "hakan"
True
>>> 1 == 1 and 1 > 0
True

test_val = "01234"
if test_val == "01234" or test_val == "0":
    print("Correct")

Assignment Operators

Up to now we’ve only been using a single assignment sign: =, the assignment operator that assigns data to a variable. Below is a table of all assignment operators — examine them and then we’ll do a few examples.

>>> a = 5
>>> a += 1 # this means a = a + 1
6
>>> a -= 1 # means a = a - 1; a's new value is 6 from the line above, so here it becomes 5 again
5
>>> a /= 2 # a = a/2
2.5

Membership Operators

The purpose of this operator is to let us query whether a value exists inside another value.

>>> "1234" in "01234" # the left value is found inside the right value, so it returns True; is 1234 in 01234?
True # yes, it is
>>> "1234" not in "0" # is 1234 not in "0"?
True # yes, it is not

Identity Operators

Every object in Python has an identity number. This identity number essentially shows the address of that object in memory. We can find the id information of objects using the built-in id() function.

>>> a = 2.5
>>> id(a) # its location in memory
1510664639136
>>> id("hello world")
1510666808640

As you can see, every value has an id number and a location. Let’s also look at the other identity operator, is:

>>> a = 1
>>> a is 1
True
>>> a = 1000
>>> a is 1000 # why did this return False?
False

The reason is that for numbers outside the range -5 to 257, Python creates a new memory allocation each time. Let me explain it this way:

>>> a = 1000 # opened a new space (address) with value 1000
>>> a is 1000 # because it opened another one here, the same value now has two different addresses — and that's why
False # we got False

The print() Function

The purpose of the print function is to write text to the screen. If you remember the brief introduction to functions lesson, functions take parameters or don’t, depending on the task they perform — just like in mathematics. The print function is one that can accept unlimited data parameters while also having its own special parameters. Whatever you pass to it as parameters, the print function will output them to the screen in order.

How to build functions with unlimited parameters is something I’ll cover in upcoming lessons.

>>> text = "Python's name does not come from the snake"
>>> print(text)
Python's name does not come from the snake
>>> text2 = """python is an "open source" language"""
>>> print(text2)
python is an "open source" language
>>> print(1, 2, 3, 4, 5, 6, 7) # used 7 parameters
1 2 3 4 5 6 7

Other Parameters in the print() Function

sep

The purpose of the sep parameter is to add something after each value written to the print function. If you write sep="0", Python will append 0 after each value you pass as a parameter to print. For example:

print(“data”, sep=“str_value”) — sep takes either None or a string value.

>>> print(1, 2, 3, 4, 5, 6, 7, sep=" - ")
1 - 2 - 3 - 4 - 5 - 6 - 7 # as you can see, a dash was added between all of them

end

The role of the end parameter is to write the object that will be appended to the end of the data given to the print function.

The end parameter also takes None or a string value.

By default, the print function has print(end=“\n”) — the newline escape character.

>>> print("I couldn't think of what to write here", end="\n") # \n is the newline escape character
I couldn't think of what to write here
>>> print("I couldn't think of what to write here", end=" - ")
I couldn't think of what to write here - >>> print("I couldn't think of what to write here", end=" - \n")
I couldn't think of what to write here -

Writing to a File Instead of the Screen with print

We’ll cover file operations in Python later, but it’s good to mention it briefly here. Normally the print function outputs to the screen, but we can change this and make it write to a file instead.

file parameter

Tells it which file to write the data to:

>>> file = open("test.txt", "w") # w = we opened our file in write mode
>>> print("writing to a file for the first time", file = file) # printed
>>> file.close() # closed

flush

The flush parameter lets us write data to the file immediately without buffering:

>>> file = open("test.txt", "w") # w = we opened our file in write mode
>>> print("writing to a file for the second time", file = file) # if you open the file right now you'll see it's empty — the write operation actually happens when you do "file.close()", but if you want it to happen immediately:
>>> print("writing to a file for the second time", file = file, flush=True) # write it like this
>>> file.close()