In this lesson, we'll look at how you can use conditional constructs to change the behavior of a program, which can be made to act based on the result of a condition it checks. This allows you to write complex programs that behave depending on the situation.

As an example, consider a function that determines the type of sentence passed to it. First, it'll distinguish between normal sentences and questions:

def get_type_of_sentence(sentence):
  last_char = sentence[-1]
  if last_char == '?':
      return 'question'
  return 'normal'

print(get_type_of_sentence('Hodor'))   # => normal
print(get_type_of_sentence('Hodor?'))  # => question

if is a language construct that controls the procedure of how instructions are executed. After the word if it passes a predicate expression, followed by a colon at the end. Next, we pass a block of code. It will execute if the predicate is true.

If the predicate is false, the code block is skipped and the function continues to be executed. In our case, the next line of code, return 'normal', will make the function return a string and terminate.

return can be anywhere in a function, even inside a code block with a condition.

Implement a function called guess_number() that takes a number and checks if the number is equal to a given number (let's say 42). If it's equal, the function should return the string 'You win!', otherwise it should return the string 'Try again!'.

guess_number(42) # You win!
guess_number(61) # Try again!