if statements

https://docs.python.org/3/tutorial/controlflow.html

INTRODUCTION

The 'if' statement is used for conditional execution. It is a compound statement.

# Compound statement structure.

header_statement:   # 'if' or 'while' or 'for'
    statements   # indentation 4 spaces (recommended)

# Nested suites in compound statements.

suite1           # no indentation
header_statement1:
    suite2       # indentation 4 spaces
    header_statement2:
        suite3   # total indentation 8 spaces
    suite2 (continued)   # indentation 4 spaces
suite1 (continued)   # no indentation

# Syntax. Zero or one part of the 'if' statement will be executed.

if condition1:
    statements
elif condition2:    # optional, more 'elif' parts is possible
    statements
else:               # optional, only one 'else' part is possible
    statements

# Short form in a single line (better to avoid).

if condition: simple_statement

assert isinstance(n, int)
if n < 0:
    print("negative number")
elif n % 2 == 0:
    print("{} {}".format(n, "is even"))
else:
    print("{} {}".format(n, "is odd"))

CONDITIONAL EXPRESSION

if condition:
    A = X
else:
    A = Y

# Conditional expression (sometimes called a “ternary operator”) [PEP 308].

A = X if condition else Y
A = ((X) if (condition) else (Y))   # for more complex expressions

# In C/C++:
# A = ((condition) ? (X) : (Y))

a, b = 25, 30
pos_a = ((-a) if a < 0 else a)   # abs(a) is better
max_ab = (b if a < b else a)   # max(a, b) is better
min_ab = (a if a < b else b)   # min(a, b) is better