Python Conditions and Branching

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Comparison operations compare values and return a boolean.

Python Comparison Operators

| Operator | Name | Example | |:---:|::|:---:| | == | Equals | 4 == 4 | | != | Not Equal | 4 != 5 | | > | Greater Than | 5 > 4 | | < | Less Than | 4 < 5 | | >= | Greater Than Or Equal To | 5 >=5 | | <= | Less Than Or Equal To | 4 <= 4|

Branching Statements

The If Statement

If statements allow for code to only execute if a condition evaluates as True.

if age > 18:
	print("You may enter the AC/DC concert.")
print("This statement will print regardless.")

Apparently, you can have brackets around the conditional:

if (age > 18):
	print("You may enter the AC/DC concert.")
print("This statement will print regardless.")

The Else Statement

The else statement executes if the conditional evaluates to false.

if age > 18:
	print("You may enter the AC/DC concert.")
else:
	print("You may enter the Meatloaf concert.")
print("This statement will print regardless.")

The Elif Statement

Elif statements allow for multiple if conditionals to be evaulated before an Else statement is triggered.

if age > 18:
	print("You may enter the AC/DC concert.")
elif age == 18:
	print("You may enter the Pink Floyd concert.")
else:
	print("You may enter the Meatloaf concert.")
print("This statement will print regardless.")

Logic Operators

Logic operators take boolean values and produce different boolean values.

| Operator | Description | Example | |:---:|::|:---:| | Not | Returns the opposite | not(True): False | | Or | Returns False only if all operands are False | if x or y or z: | | And | Returns True only if all operands are True | if x and y and z: |

Or syntax

if age > 18 or parent_present == True or snuck_in == True:
	print("You may enter the AC/DC concert.")
print("The audience is now deaf.")

And syntax

if age > 18 and parent == True and sloshed == True:
	print("You may scream at the goalie.")
print("The audience is now deaf.")

Table of Logical Operator Results

The following table illustrates the nature of the different logical operators.

The and statement is only True when both conditions are true. The or statement is true if one condition is True. The not statement outputs the opposite truth value.

Use of brackets for clarity

Given I often have trouble with logical operators in conditionals, brackets may help:

And

if(album_year > 1979) and (album_year < 1990):
    print ("Album year was in between 1980 and 1989")

Or

if(album_year < 1980) or (album_year > 1989):
    print ("Album was not made in the 1980's")

Not

if not (album_year == '1984'):
    print ("Album year is not 1984")