I'm currently in pdb trace to figure this out
ipdb> isinstance(var, Type)
False
ipdb> type(var)
<class 'module.Type'>
ipdb> Type
<class 'module.Type'>
Why can this happen?
P. S. isinstance(var, type(var)) returns True as expected
3 Answers
I can only guess, but if you do in
moduleclass Type(object): pass var = Type() class Type(object): passthen both types look like
<class 'module.Type'>, but are nevertheless different.You could check that with
print(id(Type), id(var.__class__))or with
print(Type is var.__class__)Note that these comparisons work for both old-, and new-style classes. For new-style classes, they are equivalent to
print(Type is type(var)). But this is not the case for old-style classes.Another quite common trap is that you call this module with
python -m moduleor
python module.pymaking it known as
__main__module. If it is imported somewhere else under its true name, it is known under that name as well with a different name space.Another guess could be that you are working with ABCs or otherwise let the class have a
__instancecheck__()method.
5 Comments
evgeniuz
I have defined only one Type across all of my source files. And I'm not fiddling with hidden methods. Only
__str__, __iter__, __len__. So this is not the case. Also, this class is subclass of object.evgeniuz
BTW, I'm currently in pdb session. What should I check to determine cause?
Karl Knechtel
You might consider taking a look at
id(type(var)), type(var) is Type, etc.
0 _
for old-style classes, compare
Type is var.__class__, because Type is type(var) can fail. This remains relevant, because of distutils classes that are monkey-patched by setuptools.
Connor Ferster
#2 Solved it for me. Changed
from module.sub_module.thing import SpecificThing to import module.sub_module.thing as thing and then referenced thing.SpecificThing in the code and the problem was fixed. This was fixed even though I was using IPython autoreload as described below.Users of the "autoreload" setting in iPython will probably run into this. When a class is reloaded, it will become a new class with the exact same name. Instances of the old class will not have their type updated:
# After reloading the Role class
[ins] In [19]: y = Role()
[ins] In [20]: isinstance(x, Role)
Out[20]: False
[nav] In [21]: isinstance(y, Role)
Out[21]: True
[ins] In [22]: type(x)
Out[22]: myproject.auth.Role
[ins] In [23]: type(y)
Out[23]: myproject.auth.Role
3 Comments
OverLordGoldDragon
Any option aside
imp.reload(module) and re-instantiating x? I could open a question
MCK
I had this when I used importlib.reload in the wrong order: library 1 called library 2, but I did importlib.reload for library 1 first before library 2, so every isinstance failed.
FredMaster
@Hubro you saved my life. I just ran into this problem and it took me over an hour to find your solution.
I encountered this problem as well, for me to problem laid in my imports. I imported Type once from parent.child.Type and once from child.Type. I assume that when using the full path the module is imported from the installed pip package, whereas using the relative path it is imported as a new module on the fly.
1 Comment
Community
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Type(say at different points in time). Could you produce a complete example that demonstrates the problem?import/reloadmagic in your code?print repr(var.__class__), repr(Type). I resolved the problem by changing the relative import to absolute import. I will create a code that demonstrates the problem.