Nonetype refers to an object or type whose value is null (none).
Questions tagged [nonetype]
1345 questions
994
votes
9 answers
Python `if x is not None` or `if not x is None`?
I've always thought of the if not x is None version to be more clear, but Google's style guide and PEP-8 both use if x is not None. Are there any minor performance differences (I'm assuming not), and is there any case where one really doesn't fit…
orokusaki
- 55,146
- 59
- 179
- 257
907
votes
4 answers
not None test in Python
Out of these not None tests.
if val != None:
if not (val is None):
if val is not None:
Which one is preferable, and why?
prosseek
- 182,215
- 215
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750
votes
15 answers
Return a default value if a dictionary key is not available
I need a way to get a dictionary value if its key exists, or simply return None, if it does not.
However, Python raises a KeyError exception if you search for a key that does not exist. I know that I can check for the key, but I am looking for…
Spyros
- 46,820
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661
votes
9 answers
How to "test" NoneType in python?
I have a method that sometimes returns a NoneType value. So how can I question a variable that is a NoneType? I need to use if method, for example
if not new:
new = '#'
I know that is the wrong way and I hope you understand what I meant.
CrveniZg
- 6,671
- 2
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- 8
449
votes
10 answers
Why do I get AttributeError: 'NoneType' object has no attribute 'something'?
I am getting an error message that says
AttributeError: 'NoneType' object has no attribute 'something'
How can I understand this message?
What general scenarios might cause such an AttributeError, and how can I identify the problem?
This is a…
Jacob Griffin
- 4,807
- 3
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326
votes
11 answers
remove None value from a list without removing the 0 value
This was my source I started with.
My List
L = [0, 23, 234, 89, None, 0, 35, 9]
When I run this :
L = filter(None, L)
I get this results
[23, 234, 89, 35, 9]
But this is not what I need, what I really need is :
[0, 23, 234, 89, 0, 35,…
mongotop
- 7,114
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300
votes
6 answers
Python None comparison: should I use "is" or ==?
My editor warns me when I compare my_var == None, but no warning when I use my_var is None.
I did a test in the Python shell and determined both are valid syntax, but my editor seems to be saying that my_var is None is preferred.
Is this the…
Clay Wardell
- 14,846
- 13
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264
votes
2 answers
Python void return type annotation
In python 3.x, it is common to use return type annotation of a function, such as:
def foo() -> str:
return "bar"
What is the correct annotation for the "void" type?
I'm considering 3 options:
def foo() -> None:
not logical IMO, because None…
Tregoreg
- 18,872
- 15
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- 69
209
votes
12 answers
TypeError: 'NoneType' object is not iterable in Python
What does TypeError: 'NoneType' object is not iterable mean? Example:
for row in data: # Gives TypeError!
print(row)
Alex Gordon
- 57,446
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- 1,062
176
votes
7 answers
Replace None with NaN in pandas dataframe
I have table x:
website
0 http://www.google.com/
1 http://www.yahoo.com
2 None
I want to replace python None with pandas NaN. I tried:
x.replace(to_replace=None, value=np.nan)
But I got:
TypeError: 'regex' must be a string or a…
AdamNYC
- 19,887
- 29
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- 154
127
votes
13 answers
What is a 'NoneType' object?
I'm getting this error when I run my python script:
TypeError: cannot concatenate 'str' and 'NoneType' objects
I'm pretty sure the 'str' means string, but I dont know what a 'NoneType' object is. My script craps out on the second line, I know the…
insecure-IT
- 2,068
- 4
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126
votes
5 answers
Python 3 type hinting for None?
def foo(
hello: str='world', bar: str=None,
another_string_or_None: str|????=None):
pass
I'm trying to set a type hint in Python in a function, you can add more than one type hint with something: str|bool='default value', but,…
fj123x
- 6,904
- 12
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- 58
93
votes
5 answers
Why does append() always return None in Python?
list = [1, 2, 3]
print(list.append(4)) ## WRONG, print does not work, append() returns None
## RIGHT:
list.append(4)
print(list) ## [1, 2, 3, 4]
I'm learning Python and I'm not sure if this problem is specific to the language and how append is…
starcodex
- 2,198
- 4
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- 34
81
votes
3 answers
Sort list while pushing None values to the end
I have a homogeneous list of objects with None, but it can contain any type of values.
Example:
>>> l = [1, 3, 2, 5, 4, None, 7]
>>> sorted(l)
[None, 1, 2, 3, 4, 5, 7]
>>> sorted(l, reverse=True)
[7, 5, 4, 3, 2, 1, None]
Is there a way without…
Nikolai Golub
- 3,327
- 4
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63
votes
9 answers
Python: "TypeError: __str__ returned non-string" but still prints to output?
I have this piece of code which creates a new note. When I try to print, I get the following error even though it prints the output:
Error:
C:\Python27\Basics\OOP\formytesting>python notebook.py
Memo=This is my first memo, Tag=example
Traceback…
user1050619
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