What are the differences between type() and isinstance()?

Question

What are the differences between these two code fragments?

Using type():

import types

if type(a) is types.DictType:
    do_something(         


        

Answer 1

For the real differences, we can find it in code, but I can't find the implement of the default behavior of the isinstance().

However we can get the similar one abc.__instancecheck__ according to __instancecheck__.

From above abc.__instancecheck__, after using test below:

# file tree
# /test/__init__.py
# /test/aaa/__init__.py
# /test/aaa/aa.py
class b():
pass

# /test/aaa/a.py
import sys
sys.path.append('/test')

from aaa.aa import b
from aa import b as c

d = b()

print(b, c, d.__class__)
for i in [b, c, object]:
    print(i, '__subclasses__',  i.__subclasses__())
    print(i, '__mro__', i.__mro__)
    print(i, '__subclasshook__', i.__subclasshook__(d.__class__))
    print(i, '__subclasshook__', i.__subclasshook__(type(d)))
print(isinstance(d, b))
print(isinstance(d, c))

  
 __subclasses__ []
 __mro__ (, )
 __subclasshook__ NotImplemented
 __subclasshook__ NotImplemented
 __subclasses__ []
 __mro__ (, )
 __subclasshook__ NotImplemented
 __subclasshook__ NotImplemented
 __subclasses__ [..., , ]
 __mro__ (,)
 __subclasshook__ NotImplemented
 __subclasshook__ NotImplemented
True
False

I get this conclusion, For type:

# according to `abc.__instancecheck__`, they are maybe different! I have not found negative one 
type(INSTANCE) ~= INSTANCE.__class__
type(CLASS) ~= CLASS.__class__

For isinstance:

# guess from `abc.__instancecheck__`
return any(c in cls.__mro__ or c in cls.__subclasses__ or cls.__subclasshook__(c) for c in {INSTANCE.__class__, type(INSTANCE)})

BTW: better not to mix use relative and absolutely import, use absolutely import from project_dir( added by sys.path)