This expression is true in Python: {}.keys().insert(0, “”) == None. Why?
Question
Look to my Python session:
>>> {}.keys().insert(0, "") == None
True
but:
>>> k = {}.keys()
>>> k
[]
>>> k.insert(0, "")
>>> k
['']
Why??
PS . Thanks for help! Python have very strange design - do not support chaining:
That is root of my problem...
2 answers
solution1
10 ACCPTED 2013-02-08 20:13:50
list.insert returns None ; when you print k you're printing the new state of the list.
solution2
2 2013-02-08 20:15:57
You are checking the return type to None in case 1 which would evaluate to True . Python insert returns None
The technical post webpages of this site follow the CC BY-SA 4.0 protocol. If you need to reprint, please indicate the site URL or the original address.Any question please contact:yoyou2525@163.com.
Related Question
Python function returns None. Don't quite understand why
Some (Python) dbf fields are filled with None. Why?
myRange function giving output of None. Why is this?
Python 3 Function is returning None. GCD and Euclid
This code for Web Scraping using python returning None. Why? Any help would be appreciated
Django ValidationError: ["“('1',)” value must be either True, False, or None."]
LeetCode expects null instead of None. How to do this in python?
Why does pandas “None | True” return False when Python “None or True” returns True?
Why does Python insert None into slice steps?
Python None < 0 = True?
Related Tags