Identity is not the same thing as equality in Python. In these instances, we want the latter.
Use ==/!= to compare str, bytes, and int literals.
$ __python__
```python
>>> proj = "pro"
>>> proj += 'j'
>>> proj
'proj'
>>> proj == 'proj'
True
>>> proj is 'proj'
False
>>> 0 == 0.0
True
>>> 0 is 0.0
False
```
[flake8](http://flake8.pycqa.org) testing of https://github.com/rwightman/pytorch-image-models on Python 3.7.1
$ __flake8 . --count --select=E9,F63,F72,F82 --show-source --statistics__
```
./data/loader.py:48:23: F823 local variable 'input' defined as a builtin referenced before assignment
yield input, target
^
./models/dpn.py:170:12: F632 use ==/!= to compare str, bytes, and int literals
if block_type is 'proj':
^
./models/dpn.py:173:14: F632 use ==/!= to compare str, bytes, and int literals
elif block_type is 'down':
^
./models/dpn.py:177:20: F632 use ==/!= to compare str, bytes, and int literals
assert block_type is 'normal'
^
3 F632 use ==/!= to compare str, bytes, and int literals
1 F823 local variable 'input' defined as a builtin referenced before assignment
4
```
__E901,E999,F821,F822,F823__ are the "_showstopper_" [flake8](http://flake8.pycqa.org) issues that can halt the runtime with a SyntaxError, NameError, etc. These 5 are different from most other flake8 issues which are merely "style violations" -- useful for readability but they do not effect runtime safety.
* F821: undefined name `name`
* F822: undefined name `name` in `__all__`
* F823: local variable name referenced before assignment
* E901: SyntaxError or IndentationError
* E999: SyntaxError -- failed to compile a file into an Abstract Syntax Tree
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