Nested Conditionals

Estimated Time: 15 minutes

One of the coolest things about Python is that you can use pieces of syntax in lots of situations.

The code in an if statement's body can have any valid Python.

if 5 < 15:
  print("We can do anything in here")

  possible = 10
  print("possibilities:", possible)
  possible = possible * 100
  print("possibilities:", possible)
  possible = possible * 100
  print("possibilities:", possible)
  possible = possible * 100
  print("possibilities:", possible)
  possible = possible * 100
  print("possibilities:", possible)
  print("TOO MANY POSSIBILITIES")

We can even put another if statement in the body of an if statement.

if x > 10:
  print("x is greater than 10")
  if y > 10:
    print("and, y is greater than 10")

When there's one conditional statement inside another, it's called a nested conditional. The inner conditional is nested in the outer one.

The trick to reading nested conditionals in Python is to keep careful track of the indentation. Each block keeps going until the code is no longer indented. You sometimes have to look very carefully to match up each else with the corresponding if, especially when there's lots of nesting and conditions.

Here's an example with lots of nesting:

password = input("password: ")

if len(password) > 8:
  if any(number in password for number in "0123456789"):
    if password != password.lower():
      if password != password.upper():
        print("Password valid. Account created.") 
      else:
        print("password must contain a lowercase letter")
    else:
      print("password must contain an uppercase letter")
  else:
    print("password must contain a number")
else:
  print("password too short, must be more than 8 characters.")

With this many levels of nesting, it's a little hard to tell which statement goes with which, but you can still match them up.

Copy this code to a new replit and try it out! You may have to practice using the tab key on your keyboard 😉.