ImportError Cannot import name X

Question

I have four different files named  main py  vector py  entity py and physics py  I will not post all the code  just the imports  because I think that s where the error is  If you want  I can post more   main py  import time from entity import Ent from vector import Vect  the rest just creates an entity and prints the result of movement  entity py  from vector import Vect from physics import Physics class Ent       holds vector information and id def tick self  dt        this is where physics changes the velocity and position vectors  vector py  from math import   class Vect       holds i  j  k  and does vector math  physics py  from entity import Ent class Physics       physics class gets an entity and does physics calculations on it   I then run from main py and I get the following error   Traceback  most recent call last   File  quot main py quot   line 2  in  lt module gt      from entity import Ent File  quot     entity py quot   line 5  in  lt module gt      from physics import Physics File  quot     physics py quot   line 2  in  lt module gt      from entity import Ent ImportError  cannot import name Ent   I m guessing that the error is due to importing entity twice  once in main py  and later in physics py  but I don t know a workaround  Can anyone help

User · Answer

In my case  I was working in a Jupyter notebook and this was happening due the import already being cached from when I had defined the class function inside my working file    I restarted my Jupyter kernel and the error disappeared

User · Answer

You have circular dependent imports  physics py is imported from entity before class Ent is defined and physics tries to import entity that is already initializing  Remove the dependency to physics from entity module

User · Answer

If you are importing file1 py from file2 py and used this   if   name         main           etc   Variables below that in file1 py cannot be imported to file2 py because   name   does not equal   main      If you want to import something from file1 py to file2 py  you need to use this in file1 py   if   name       file1         etc   In case of doubt  make an assert statement to determine if   name       main

User · Answer

This is a circular dependency  It can be solved without any structural modifications to the code  The problem occurs because in vector you demand that entity be made available for use immediately  and vice versa  The reason for this problem is that you asking to access the contents of the module before it is ready -- by using from x import y  This is essentially the same as  import x y   x y del x   Python is able to detect circular dependencies and prevent the infinite loop of imports  Essentially all that happens is that an empty placeholder is created for the module  ie  it has no content   Once the circularly dependent modules are compiled it updates the imported module  This is works something like this   a   module     import a    rest of module  a update contents real a    For python to be able to work with circular dependencies you must use import x style only   import x class cls      def   init   self           self y   x y   Since you are no longer referring to the contents of the module at the top level  python can compile the module without actually having to access the contents of the circular dependency  By top level I mean lines that will be executed during compilation as opposed to the contents of functions  eg  y   x y   Static or class variables accessing the module contents will also cause problems

User · Answer

Don t see this one here yet - this is incredibly stupid  but make sure you re importing the correct variable function   I was getting this error     ImportError  cannot import name IMPLICIT WAIT   because my variable was actually IMPLICIT TIMEOUT   when I changed my import to use the correct name  I no longer got the error

User · Answer

While you should definitely avoid circular dependencies  you can defer imports in python   for example   import SomeModule  def someFunction arg       from some dependency import DependentClass   this   at least in some instances   will circumvent the error

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Not specifically for this asker  but this same error will show if the class name in your import doesn t match the definition in the file you re importing from

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Also not directly relevant to the OP  but failing to restart a PyCharm Python console  after adding a new object to a module  is also a great way to get a very confusing ImportError  Cannot import name       The confusing part is that PyCharm will autocomplete the import in the console  but the import then fails

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The problem is clear  circular dependency between names in entity and physics modules   Regardless of importing the whole module or just a class  the names must be loaded    Watch this example     a py import b def foo      pass b bar       b py import a def bar      pass a foo     This will be compiled into     a py   import b   b py   import a   ignored  already importing def bar      pass a foo     name a foo is not defined      import b done  def foo      pass b bar     done      With one slight change we can solve this     a py def foo      pass import b b bar       b py def bar      pass import a a foo     This will be compiled into     a py def foo      pass   import b   b py def bar      pass   import a   ignored  already importing a foo     import b done  b bar     done

User · Answer

This is a circular dependency   we can solve this problem by using import module or class or function where we needed  if we use this approach  we can fix circular dependency  A py  from B import b2 def a1        print  a1       b2     B py  def b1       from A import a1    print  b1      a1    def b2       print  b2   if   name         main        b1

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One way to track import error is step by step trying to run python on each of imported files to track down bad one    you get something like   python   main py      ImportError  cannot import name A  then you launch   python   modules a py      ImportError  cannot import name B  then you launch   python   modules b py      ImportError  cannot import name C  some NON-Existing module or some other error

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To make logic clear is very important  This problem appear  because the reference become a dead loop    If you don t want to change the logic  you can put the some import statement which caused ImportError to the other position of file  for example the end   a py  from test b import b2  def a1        print  a1       b2     b py  from test a import a1  def b1        print  b1       a1    def b2        print  b2    if   name         main         b1        You will get Import Error  ImportError  cannot import name  a1    But if we change the position of from test b import b2 in A like below   a py  def a1        print  a1       b2    from test b import b2   And the we can get what we want   b1 a1 b2

User · Answer

As already mentioned  this is caused by a circular dependency  What has not been mentioned is that when you re using Python typing module and you import a class only to be used to annotate Types  you can use Forward references       When a type hint contains names that have not been defined yet  that   definition may be expressed as a string literal  to be resolved later    and remove the dependency  the import   e g  instead of  from my module import Tree  def func arg  Tree         code   do   def func arg   Tree          code    note the removed import statement

User · Answer

I just got this error too  for a different reason     from my sub module import my function   The main script had Windows line endings  my sub module had UNIX line endings  Changing them to be the same fixed the problem  They also need to have the same character encoding

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Don t name your current python script with the name of some other module you import  Solution  rename your working python script  Example    you are working in medicaltorch py in that script  you have  from medicaltorch import datasets as mt datasets where medicaltorch is supposed to be an installed module   This will fail with the ImportError  Just rename your working python script in 1

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In my case  simply missed filename  from A B C import func a  x  from A B C D import func a  O  where D is file

[python] ImportError: Cannot import name X

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