I am new to python. I am using the anaconda prompt to run my code. I am trying to import a class from another module but I keep getting errors such as cannot find reference to the class.
P.S please don't negative mark this, or else I will lose the privilege of asking questions
I have already provided an __init__ function.
The module itself runs just fine.
I have used from parser import Parser
I have used from parser import * statement as well
My Parser class
class Parser(object):
def __init__(self, tokens):
self.tokens = tokens
self.token_index = 0
My main class
from parser import Parser
I expected it to normally import the class, but it is unable to.
I keep getting the cannot import name 'Parser' from 'parser' (unknown location) when I use from parser import Parser
parser is also the name of a Python module in the standard library.
It's likely there is a name conflict, and that Python is importing the module from the standard library.
I changed the module name to mparser and it works!
Related
this is such a simple problem but I cant seem to find any direct explanation to this.
in module.py
def foo():
print("foo")
in main.py
import module
foo()
it will result in an error saying that foo is not defined? when i look for the answer online, I can't find anything surprisingly
I'm not planning to use things like
from x import y
just straight up the import system
When you import an external module, it generates a variable named module that contains all classes, functions and variables from the module. To acess 'foo' function you need to first acess the module:
module.foo()
To import 'foo' function you can import everything from the module, like this:
from module import *
Now you can simply do: foo()
You can also set a custom name to the module, like:
import module as M
And now you can run 'foo' like this:
M.foo()
PS: I'm not english native
The statement
import module
makes the name of module module available. So you can use module.foo().
If you want to call foo() without "qualifying" it:
from module import foo
or
from module import *
but that latter is bad idea because you are liable to import unexpected names, which may collide with other names you imported from other modules.
from model import foo
is the preferred way as in any kinds of
from model import *
you (and anyone ever working on that code) has no idea what has been imported. Could even lead to name conflicts.
I would like to make an imported module behave like an object, ie. an dictionary.
E.g.
import module
print(module['key'])
and in module.py
return {'key':'access'}
This is very easy for Class by inheriting from dict, but how do I do this on a module level?
In particular I want to dynamically built the dictionary in module and return it when module is imported.
I know that there are other solutions such as defining the dict as a var in the module workspace and accessing it via module.var, but I am interested if something like this is possible.
As you point out, you can do this with a class, but not with a module, as modules are not subscriptable.Now I'm not going to ask why you want to do this with an import, but it can be done.
What you do is create a class that does what you want, and then have the module replace itself with the class when imported. This is of course a 'bit of a hack' (tm). Here I'm using UserDict as it gives easy access to the dict via the class attr data, but you could do anything you like in this class:
# module.py
from collections import UserDict
import sys
import types
class ModuleDict(types.ModuleType, UserDict):
data = {'key': 'access}
sys.modules[__name__] = ModuleDict(__name__)
Then you can import the module and use it as desired:
# code.py
import module
print(module['key']
# access
I want to do the semantic checking for a language and i use ANTLR4 to generate parser and visitor class. However i met a problem.
If i use this method print(type(newList[0].expression()))
I will get a type like this <class 'IDILParser.IDILParser.IdenetExpressionContext'>
However, if i run the code below, i will get a error like this NameError: name 'IDILParser' is not defined
Can i ask how to fix this problem? Thanks!
from antlr4 import *
if __name__ is not None and "." in __name__:
from .IDILParser import IDILParser
else:
from IDILParser import IDILParser
class IDILVisitor(ParseTreeVisitor):
def visitAssign(self, ctx:IDILParser.AssignContext):
if type(newList[0].expression()) is IDILParser.IDILParser.IdenetExpressionContext:
...
You did from IDILParser import IDILParser, which means the IDILParser in your code already acutally refers to IDILParser.IDILParser.
So try taking away that one layer:
if type(newList[0].expression()) is IDILParser.IdenetExpressionContext:
...
Btw, when in doubt if your code is being run as a module or as a script (aka relative imports do work or not), you could also do the following:
try:
from .IDILParser import IDILParser
except ImportError:
from IDILParser import IDILParser
I am a new comer when it comes to package and module to python.
I am trying to cut my script in several separate compartiment. to improve readability and maintenance.
My problem is the following:
I have a module which define a class and a function inside this module which instantiate this class.
module blast.py
class Blast():
blabla
def foo():
blast = Blast()
# do some stuff
this module is inside a package with a _ _init__.py file
__all__ = ["blast"]
I have a main script In which i want to use that function.
I import the module with
from package import blast
But To use that function I have to use the name space of the module ( at least my IDE say me that: pycharm)
blast.foo()
So does it works? does the function will see the class inside it module?
And more generally Could I import some function of my package inside my namespace. I though it was done this way and answer I got from internet doesn't really help me.
Yes, the function blast.foo() would know and find the class Blast.
Whenever you import a module, in part or in its entirety, the entire module is loaded - the way you import it merely decides on what classes and functions are available in the current scope, and in what way.
For example, if you call this:
from package.blast import foo
only the function foo() would be available, but the entire package read and loaded. if you were to try instantiate the class Blast by itself in the same script, this would not work.
By the way, you can make importing functions more convenient, if you customize __init__.py. In your case, if you were to edit it like so:
>>>__init__.py
from blast.py import Blast, foo
you can import both function and class like so:
from package import Blast, foo
The reason why you __all__ parameter does not work, is because it requires another import statement - mainly this:
from package import *
Calling this with your current __init__.py should work as expected.
Perhaps this post by Mike Grouchy is able to clarify things a bit more.
Given this simple folder structure
/main.py
/project/a.py
/project/b.py
main.py is executed by the python interpreter and contains a single line, import project.a.
a and b are modules, they need to import each other. A way to achieve this would be
import project.[a|b]
When working with deeper nested folder structures you don't want to write the entire path everytime you use a module e.g.
import project.foo.bar
project.foo.bar.set_flag(project.foo.bar.SUPER)
Both from project import [a|b] and import project.[a|b] as [a|b] result in an import error (when used in both, a and b).
What is different between the standart import syntax and the from or as syntax? Why is only the standart syntax working for mutual imports?
And more importantly, is there a simple and clean way to import modules that allows mutual imports and assigning shorter names to them (ideally the modules basename e.g. bar in the case of project.foo.bar)?
When you do either import project.a or from project import a, the following happens:
The module object for project.a is placed into sys.modules. This is a dictionary that maps each module name to its module object, so you'll have sys.modules = {..., 'p.a': <module 'p.a' from '.../project/a.py'>, ...}.
The code for the module is executed.
The a attribute is added to project.
Now, here is the difference between import project.a and from project import a:
import project.a just looks for sys.modules['project.a']. If it exists, it binds the name project using sys.modules['project'].
from project import a looks for sys.modules['project'] and then checks if the project module has an a attribute.
You can think of from project import a as an equivalent to the following two lines:
import project.a # not problematic
a = project.a # causes an error
That why you are seeing an exception only when doing from project import a: sys.modules['project.a'] exists, but project does not yet have a a attribute.
The quickest solution would be to simply avoid circular imports. But if you can't, then the usual strategies are:
Import as late as possible. Suppose that your a.py looks like this:
from project import b
def something():
return b.something_else()
Rewrite it as follows:
def something():
from project import b
return b.something_else()
Of course, you would have to repeat imports in all your functions.
Use lazy imports. Lazy imports are not standard feature of Python, but you can find many implementations around. They work by using the "import as late as possible" principle, but they add some syntactic sugar to let you write fewer code.
Cheat, and use sys.modules, like this:
import sys
import project.a
a = sys.modules['project.a']
Very un-pythonic, but works.
Obviously, whatever solution you choose, you won't be able to access the attributes from a or b until the modules have been fully loaded.