Branching

doing "what-if" conditionals on Python

if statements

In Python, we can branch using a relatively understandable syntax:

if myVariable == "value" :
    # do something

Keep in mind that:

• == compares the left side and the right side

• = simply assigns the right side to the left side!

# this will work
myVariable = 10 

# this will also work
if myVariable == 10: 
    print("myVariable is 10")
    
# this will not work, will print out a SyntaxError
if myVariable = 10:
    print("myVariable is 10")

Operators

In place of == we can also use != >=, >, < and <=:

if temperature >= 100 :
    print("Water will boil!")

if temperature > 0:
    print("Water will melt!")
    
if temperature < 0:
    print("Water will freeze!")
    
if temperature <= -273.15 : 
    print("No such temperature can exist!")

Logic

We can combine operations with the and (as well as the or and not) keywords:

batting_average = 0.320
home_runs = 25

if (batting_average > 0.300) and (home_runs >= 20):
  print("This batter should be an all-star!")
  
if not (batting_average > 0.300) and not (home runs >= 20):
  print("This batter should not be considered an all-star!")

else statements

For binary (yes-and-no) conditions, we can use the else keyword to reduce the number of if statements:

if (batting_average > 0.300) and (home_runs >= 20):
  print("This batter should be an all-star!")
else: 
  print("This batter should not be considered an all-star!")

elif statements

For n-ary (more than two) conditions, we can use if, elif and else:

if (screen_size >= 1440):
    print("Large desktop!")
elif (screen_size >= 1024) and (screen_size < 1440):
    print("Small desktop!")
elif (screen_size > 768) and (screen_size < 1024): 
    print("Tablet size!")
else:
    print("Mobile size!")