Conditional Logic

if, elif, else

if executes code if the condition is True.
If if is False, elif checks condition(s) in order (there can be multiple elif statements).
else runs only if all previous conditions are False.

Combine checks

Use and, or, not to combine conditions.

Truthy & Falsy

In Python, most values are considered truthy.
Exceptions (considered falsy): None, False, numbers equal to zero, and empty data types ([], {}, '', etc.).

is_old = 'hello'            # truthy
is_licensed = 0             # falsy

print(bool(is_old))         # True
print(bool(is_licensed))    # False


if is_old and is_licensed:              #if true and true print code
    print('you can drive now')
elif is_licensed:                       #elif print this
    print('you can\'t')
else:                                   #else print this
    print('you can\'t')

Ternary Operator (Conditional Expression)

A shorthand way to write conditional logic. Syntax: value_if_true if condition else value_if_false Does not support elif.

is_friend = False
can_message = 'message allowed' if is_friend else "not allowed to message"

print(can_message)

Short Circuiting

Python stops evaluating logical expressions once the result is determined.

With or: stops at the first True.
With and: stops at the first False

— it doesn’t evaluate the rest of the expression unnecessarily.

Using 'or' → stops when it finds the first True

x = True or print("This won't run")    #(nothing printed, because True is enough to decide result)

Using 'and' → stops when it finds the first False

y = False and print("This won't run")   #(nothing printed, because False is enough to decide result)

not Operators

Returns the opposite Boolean value.

print(not False)
print(not True)

== vs is

== checks Value equality
is checks Object identity (same memory reference)

(is) checks, whether this is in the same memory space, same bookshelf as that one

print(True is 1)    #checks for exact same thing, located in different memory space

print(True == 1)    #checks for the values

Logical Operator

<, >, ==, >=, <=, !=
and, or, not, is
Used in conditional logic to control program flow.

In Python, they let the program skip or execute lines depending on whether conditions are True or False.

Walrus Operator(:=)

Assigns values within expressions.
to do something based on a condition and then calculate that value again.

a = 'hellooooooo'

if (n := len(a)) > 10:
    print(f'the elements {n} are too long')

while ((n:= len (a)) > 1):
    print(n)
    a = a[:-1]
print(a)