How to condense if/else into one line in Python? [duplicate]

Question

This question already has answers here:

Does Python have a ternary conditional operator? (32 answers)

Closed 2 years ago.

How might I compress an if/else statement to one line in Python?

• TheZ: stackoverflow.com/questions/1686390/… docs.python.org/reference/compound_stmts.html
• Kijewski: That's the question you wanted to link: stackoverflow.com/questions/394809/python-ternary-operator
• clwen: another reference: stackoverflow.com/questions/7778400/…
• Levon: This is the question I was thinking of: stackoverflow.com/questions/11491944/…
• Brent Bradburn: Conditional expressions don't cover all cases (or all versions). Now what?

Answer 1

An example of Python's way of doing "ternary" expressions:

i = 5 if a > 7 else 0

translates into

if a > 7:
 i = 5
else:
 i = 0

This actually comes in handy when using list comprehensions, or sometimes in return statements, otherwise I'm not sure it helps that much in creating readable code.

The readability issue was discussed at length in this recent SO question better way than using if-else statement in python.

It also contains various other clever (and somewhat obfuscated) ways to accomplish the same task. It's worth a read just based on those posts.

• technazi: How do i use it in the return statement? return count if (count * (distance < within_radius)) > 0 else (continue)
• Dan Li: How can I use a boolean list in between? list = 5 if [boolean list] else 0?

Answer 2

Python's if can be used as a ternary operator:

>>> 'true' if True else 'false'
'true'
>>> 'true' if False else 'false'
'false'

• Alexander Samoylov: Just want to add the "true" command-line one-line syntax for the that. I have searched a lot how to do that, but no one answer contains this information: $ python -c "import sys; var=1; [ sys.stdout.write('POS\n') if var>0 else sys.stdout.write('NEG\n')]"

Answer 3

Only for using as a value:

x = 3 if a==2 else 0

or

return 3 if a==2 else 0

• BrenBarn: This is not restricted to assignment. It can be used in any expression.

Answer 4

There is the conditional expression:

a if cond else b

but this is an expression, not a statement.

In if statements, the if (or elif or else) can be written on the same line as the body of the block if the block is just one like:

if something: somefunc()
else: otherfunc()

but this is discouraged as a matter of formatting-style.