How to use ternary conditional operator in Python?

Python's ternary is written as a conditional expression, and its word order differs from most other languages: the value comes first, then the condition.

The syntax

value_if_true if condition else value_if_false

A concrete example:

age = 20
status = 'adult' if age >= 18 else 'minor'
print(status)     # adult

Read it left to right as: use 'adult' — if age >= 18 — otherwise 'minor'.

Python has no ? : operator

This is the single most common mistake:

status = age >= 18 ? 'adult' : 'minor'    # SyntaxError

? : is C, C++, Java, JavaScript, and PHP syntax. Python deliberately uses English keywords instead, so pasting a C-style ternary into Python raises a SyntaxError.

It is an expression, not a statement

Because it evaluates to a value, you can use it anywhere a value is allowed:

# In an assignment
discount = 0.2 if is_member else 0.0
 
# As a function argument
print('yes' if flag else 'no')
 
# Inside an f-string
message = f"{count} item{'s' if count != 1 else ''}"
 
# Inside a list comprehension
clamped = [x if x > 0 else 0 for x in numbers]

Note the comprehension case: the ternary goes before the for. An if placed after the for is a filter and means something different:

[x if x > 0 else 0 for x in numbers]   # transform: keeps every element
[x for x in numbers if x > 0]          # filter: drops non-matching elements

The else is mandatory

x = 1 if cond          # SyntaxError — no else
x = 1 if cond else 2   # valid

A conditional expression must always produce a value, so both branches are required. If you only want a side effect, use a normal if statement.

Branches must be expressions

You cannot put statements such as return, raise, or an assignment inside a branch:

# Valid — the return wraps the whole expression
def pick(cond, a, b):
    return a if cond else b

When not to use it

Chaining is legal but degrades quickly:

# Hard to scan
label = 'low' if n < 10 else 'mid' if n < 100 else 'high'

Past two conditions, prefer an explicit block:

if n < 10:
    label = 'low'
elif n < 100:
    label = 'mid'
else:
    label = 'high'

Related: the or idiom

For "use this unless it is falsy", or is often shorter:

name = user_input or 'anonymous'

Be careful: this treats 0, '', and [] as falsy. When only None should trigger the fallback, be explicit:

name = user_input if user_input is not None else 'anonymous'