That's because c hasn't finished loading at the time c. Let me say at the outset that I don't think I can get rid of circular imports altogether. Simply that mod1 can refer to objects in mod2, and mod2 can refer to objects in mod1. I placed 'import' statements in the main module, and it worked. In this case, create a file named math. Go ahead and try running the code to see this in action! In my case, my program started as a single module.
True in principle, but what if the resulting module is 1000 lines long? Python then resumes compiling Y. So I suspect a bug. Module B imports A which does nothing because A is already partially imported and then defines a class that depends on the class that is defined in module A. When Python reaches the import Y statement, it loads the code for Y, and starts executing it instead. That's because names in the 1st are not yet available, because the first module is busy importing the 2nd. Just trying to think about how it ought to work with a importing c but then c and d importing each other makes my brain hurt.
At this time, Python has installed module objects for both X and Y in sys. Import modules at the top of a file. You shouldn't use circular imports. Perhaps because it would then be too big and unwieldy to maintain? The module registry is a table of modules that have been initialized and indexed by module name. Suppose you have two functions a. I couldn't say what without looking at both entire classes. Why is this design bad? This got a bit hairy! The original project is very poorly organized.
Figuring out a way to set the attribute in the parent package and then roll it back later if the import fails is still likely to be the more robust approach. They force you to spend time being careful not to trip over them, and on top of that are a code smell that your design needs refactoring. I realise that it is up to me to avoid any name clashes. But now I have another question: Can I execute an script inside subpackage1 importig modules from subpackage2? Introducing circular references can often come up when trying to implement connection pooling, whereby a number of network connections are collected and reused by a process. I often use callbacks to get away from mutual dependencies. The most likely solution to the problem would be to change the attribute on the parent package to be handled in a fashion closer to the way the sys. However, if your code is well maintained and modularized properly, importing just a portion from the module can be quite handy and more succinct.
Note that the Reference manual is silent about such cases. How can I make this thing work? Because you're only importing the module at import-time, you don't care than the class inside it isn't defined yet. So, if the object has wrong type i should backtrace all propagation which can be quite impossible. Guido van Rossum recommends avoiding all uses of from import. It's natural for the team code to rely on user whilst the user does something with team. Tree data structures, for instance, should use weak references for their parent and sibling references if they need them! At this time, Python has installed module objects for both X and Y in sys.
This note tries to sort out some of the more common issues related to import and from-import and everything. Is there any way to force python to accept these imports for now? If the behaviour of Jim's code is officially undefined, then the docs need to say so. The problem is that you might define your own function or a top level variable that has the same name as one of the items you imported and if you try to use the one from the os module, it will use yours instead. A deeper analysis of the program could have concluded that the dependency isn't actually required, or that the depended functionality can be moved to different modules that wouldn't contain the circular reference. Study documentation for the and the module. It is not uncommon for me to find that a method in Module A needs to access something in Module B, and a method in Module B needs to access something in Module A.
In your case, only a fraction of the classes Complaint and Complainant are interdependent. Is there anything that prevent you from doing this? We can call all of the modules methods the same way before, but with the new name. This is not what happens. So I suspect a bug. I might then be lazy and not resolve the design problem, but it would continue to disturb me. Josef Meile wrote: Circular import does not work on module level, but you can import the module in a method: file1.
Python isn't Java, you don't need to put every class in its own file. This means that there is only one object the list , and both x and y refer to it. You can do it from the shell prompt by running compileall. In addition to the bug checking that PyChecker performs, Pylint offers some additional features such as checking line length, whether variable names are well-formed according to your coding standard, whether declared interfaces are fully implemented, and more. By the time you get around to using the class, it will be. Then I found the need for some modules to refer to objects in other modules, so I needed 'import' statements within the modules.
UnboundLocalError: local variable 'x' referenced before assignment This is because when you make an assignment to a variable in a scope, that variable becomes local to that scope and shadows any similarly named variable in the outer scope. You might use optional imports to support multiple versions of software or for speed ups, for example. If you want to reply to this, please follow the same practice. I will stick to my hack of putting the package name in sys. If that object is changed, like the dictionary in this example, subsequent calls to the function will refer to this changed object. Incidentally, this trick is also handy if you want to decide dynamically e.
Obviously, freeze requires a C compiler. This will usually solve the problem. If you're not careful and you have a circular dependency in your code, it can be very difficult to debug the many potential problems it causes. For example, if you have a function that does something: Delegation is an object oriented technique also called a design pattern. When Python imports a module, it first checks the module registry sys. This is will cause you to lose karma rapidly, but sometimes is necessary.