{"id":117807,"date":"2020-09-10T10:46:10","date_gmt":"2020-09-10T10:46:10","guid":{"rendered":"https:\/\/blog.finxter.com\/?p=12900"},"modified":"2020-09-10T10:46:10","modified_gmt":"2020-09-10T10:46:10","slug":"python-one-line-if-not-none","status":"publish","type":"post","link":"https:\/\/sickgaming.net\/blog\/2020\/09\/10\/python-one-line-if-not-none\/","title":{"rendered":"Python One Line If Not None"},"content":{"rendered":"

To assign the result of a function get_value()<\/code> to variable x<\/code> if it is different from None<\/code>, use the Walrus operator if tmp := get_value(): x = tmp<\/code> within a single-line if block. The Walrus operator assigns the function’s return value to the variable tmp<\/code> and returns it at the same time, so that you can check and assign it to variable x<\/code> subsequently. <\/p>\n

Problem<\/strong>: How to assign a value to a variable if it is not equal to None<\/code>—using only a single line of Python code? <\/p>\n

Example<\/strong>: Say, you want to assign the return value of a function get_value(), but only if it doesn’t return None. Otherwise, you want to leave the value as it is. Here’s a code example:<\/p>\n

import random def get_value(): if random.random()>0.5: return None return 1 # Naive approach:\nx = 42\ntmp = get_value()\nif tmp != None: x = tmp\nprint(tmp)<\/pre>\n
While this works, you need to execute the function get_value()<\/code> twice which is not optimal. An alternative would be to assign the result of the get_value()<\/code> function to a temporary variable to avoid repeated function execution:<\/p>\n
x = 42\ntemp = get_value()\nif temp != None: x = temp\nprint(x)<\/pre>\n
However, this seems clunky and ineffective. Is there a better way?<\/p>\n
Let’s have an overview of the one-liners that conditionally assign a value to a given variable:<\/p>\n