Control flow

if…elif..else Statement

  • We use if statement to run code if a certain condition is true.
  • To add more conditions, we use elif statement.
  • We can add a default code with else statement.
if condition:
    # do thing1
elif condition2:
    # do thing2
    # do thing3

For example

a = 50
b = 35
if b > a:
  print("b is greater than a")
elif a == b:
  print("a and b are equal")
  print("a is greater than b")


Relational operators

We can create boolean expressions using relational operators:

  • Equal: ==
  • Not equal: !=
  • Greater than: >
  • Less than: <
  • Greater than or equal to: >=
  • Less than or equal to: <=

Boolean operators: and, or, and not.

  • The and operator takes two arguments, and evaluates as True if both of its arguments are True. Otherwise, it evaluates to False.
  • The or operator also takes two arguments. It evaluates to True if either (or both) of its arguments are True, and False if both arguments are False.
  • not only takes one argument, and inverts it. The result of not True is False, and not False goes to True.

Try and Except Statements

We can use try and except statements to check for possible errors that a user might encounter.

    # some statement
except ErrorName:
    # some statement
  print("The 'try except' is finished")
  • The try block lets you test a block of code for errors.
  • The except block lets you handle the error.
  • The finally block lets you execute code, regardless of the result of the try- and except blocks.

Explanation First, the statement under try will be executed. If there’s an error such as NameError or a ValueError, and try statement will terminate and the except statement will execute.

def divides(a,b):
    result = a / b
    print (result)
  except ZeroDivisionError:
    print ("Can't divide by zero!")