Zain Aftab

Zain Aftab

Computer scientist who loves to read about different topics and write about different topics. 80% of my body is made of videogames.

Looping in Python

2 minute read

There are two major types of loops in Python, for loops and while loops.

For Loops

  • The for loop example below runs the print statement five times.
  • Indentation rule is the same as if statements.
  • The range function controls how many times the code in the loop is run.
for i in range(5):
    print("I must not tell lies.")
  • You can use the range function in many different ways to control the loop. Some examples are given below.

# Printing 0-9 on screen
for i in range(10):
    print(i)

# Printing 1-10 on screen
for i in range(1, 11):
    print(i)

# Increments in range

# Two ways to print the even numbers 2 to 10
for i in range(2,12,2):
    print(i)

for i in range(5):
    print((i + 1) * 2)

Nesting For Loops

  • Indent to nest loops. Example is given below.
for i in range(3):
    print("a")
    for j in range(3):
        print("b")

print("Done")

Keeping a Running Total

  • A common operation in working with loops is to keep a running total.
total = 0
for i in range(5):
    new_number = int(input("Enter a number: " ))
    total += new_number
print("The total is: ", total)

While Loops

  • A while loop is used when a program needs to loop until a particular condition occurs.
  • The range function only works with the for loop. Do not use it with the while loop!
# Printing 0 to 9
i = 0
while i < 10:
    print(i)
    i = i + 1

Increments in Python

  • i = i + 1 and i += 1 are the same.
  • Also can be used for subtraction and multiplication e.g. ’-=’

Random Numbers

  • To use random numbers, the first thing that should appear at the top of the program is an import statement: import random
  • It is important not to create a file with the same name as what is being imported. Creating a file called random.py will cause Python to start importing that file instead of the system library that creates random numbers.
  • Random numbers can be created using the randrange function.

# Random number from 0 to 10
my_number = random.randrange(11)

# Random number from 100 to 200
my_number = random.randrange(100, 201)

# Picking a random item out of a list
my_list = ["Ellie", "Abby", "Fat Geralt"]
random_index = random.randrange(3)
print(my_list[random_index])
  • If you want a random floating point number, use the random function. An example is given below:

# Random floating point number from 0 to 1
my_number = random.random()

# Random floating point number between 10 and 15
my_number = random.random() * 5 + 10

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