wait, wut?

Control Flow

Control Flow

Conditional Statements

if

  • branch execution based on value of expression
  • expression used in if statement will be converted to a boolean as if bool() constructor had been used
  • basic syntax:
if expression:
    block # block is terminated by blank line


if True:
    print("It's true!")

#=> It's true!

else clause

h = 42
if h > 50:
    print("Greater than 50")
else:
    print("50 or smaller")

#=> 50 or smaller

elif clause

h = 42
if h > 50:
    print("Greater than 50")
elif h < 20:
    print("Less than 20")
else:
    print("Between 20 and 50")

#=> Between 20 and 50

Loops

while Loop

  • similarly as in if statements, passed expression is implicitly converted to boolean
  • basic syntax:
while expression:
    block # block is terminated by blank line


c = 5
while c != 0:
    print(c)
    c -= 1 # augmented assignment operator

#=> 5
#=> 4
#=> 3
#=> 2
#=> 1

# because `c` will eventually equal 0, can replace above example with:
c = 5
while c:
    print(c)
    c -= 1

# however, this is probably not preferable because "explicit is better than implicit"

break keyword

  • many languages support loop construct ending in predicate test
  • C, C++, C#, Java, Ruby, and others have do-while
  • other languages have "repeat until" loops instead
  • NOTE: does not exist in Python; idiom is to use while True and break (using break to facilitate early exit)
    • break jumps out of inner-most executing loop to line immediately after it
  • basic usage:
while True:
    response = input() # built-in `input` function used to request string from user
    if int(response) % 7 == 0:
        break
Made with Gatsby G Logo