This question is a bit dumb but I have to know it. Is there any way to use imported modules inside other imported modules?
I mean, if I do this:
-main file-
import os
import othermodule
othermodule.a()
-othermodule-
def a():
return os.path.join('/', 'example') # Without reimporting the os module
The os module is not recognized by the file. Is there any way to "reuse" the os module?
There's no need to do that, Python only loads modules once (unless you unload them).
But if you really have a situation in which a module can't access the standard library (care to explain???), you can simply access the os module within the main module (e.g. mainfile.os, modules are just variables when imported into a module namespace).
If the os module is already loaded, you can also access it with sys.modules["os"].
You have to put import os in othermodule.py as well (or instead, if "main file" doesn't need os itself). This is a feature; it means othermodule doesn't have to care what junk is in "main file". Python will not read the files for os twice, so don't worry about that.
If you need to get at the variables in the main file for some reason, you can do that with import __main__, but it's considered a thing to be avoided.
If you need a module to be reread after it's already been imported, you probably should be using execfile rather than import.
Python only imports a module once. Any subsequent import calls, just access the existing module object.
Related
I would like to import a module from inside a functions. For example from this:
from directory.folder.module import module
def import():
app.register_blueprint(module)
To this:
def import():
from directory.folder.module import module
But, without hardcoding it. For example:
def import():
m = "module"
from directory.folder.m import m
Is it possible? Thanks in advance
You want the importlib module.
Here's the most simplistic way to use this module. There are lots of different ways of weaving the results of calls to the module into the environment:
import importlib
math = importlib.import_module("math")
print(math.cos(math.pi))
Result:
-1.0
I've used this library a lot. I built a whole plug-in deployment system with it. Scripts for all the various deploys were dropped in directories and only imported when they were mentioned in a config file rather than everything having to be imported right away.
Something I find very cool about this module is what's stated at the very top of its documentation:
The purpose of the importlib package is two-fold. One is to provide the implementation of the import statement (and thus, by extension, the import() function) in Python source code.
The intro in the 2.7 docs is interesting as well:
New in version 2.7.
This module is a minor subset of what is available in the more full-featured package of the same name from Python 3.1 that provides a complete implementation of import. What is here has been provided to help ease in transitioning from 2.7 to 3.1.
No, python import does not work this way.
Such as an example you try to import a module named mod, so you run import mod. Now interpreter will search for mod.py in a list of directories gathered from the following sources:
The directory from where the input script was run or the current directory if the interpreter is being run interactively.
The list of directories contained in the PYTHONPATH environment variable, if it is set. (The format for PYTHONPATH is OS-dependent but should mimic the PATH environment variable.)
An installation-dependent list of directories configured at the time Python is installed.
So if you have a variable named m='mod' and run import m it will search for m.py not mod.py.
But just a silly dangerous workaround is to use exec() (WARNING FOR MALICIOUS INPUT)
m = "module"
exec(f'from directory.folder.m import {m}')
If you don't mind external modules try importlib.
You can use the importlib module to programmatically import modules.
import importlib
full_name = "package." + "module"
m = importlib.import_module(full_name)
I want to put my interactive commands in a script, but I can't run the same commands in the script.
We are using a heavily packaged version of Python for our tests, we usually run tests in interactive mode, but now I want to place all the commands in a package. Below is an example using the time package.
In interactive mode:
>>> import time
>>> import myscript
In my script:
time.sleep(5)
I expected the script to refer to the globally imported packages and allow me to run sleep, but it says NameError: global name 'time' is not defined
How do I get my script to recognize all packages imported into the interactive terminal? We use thousands of packages in our toolkit, and I can't import them all into my script.
You have to import these libraries also in the .py file where you are going to use them. Python does not allow using them when they are imported in a higher level module, and that's the way it should be. Python, in some way, forces you being better programmer. Your script should be something like this:
import time
time.sleep(5)
If I have Module A:
import time
and Module B:
import A
then in module B I do have access to libraries that A imported, but they must be qualified thus:
A.time.sleep5()
In short, when you import a module, the public names in that module become accessible to the importer. But what you are attempting to do is quite different. In essence, you have Module A as:
import time
import B
And module B as:
time.sleep(5)
Module B neither directly imports the time package nor module A and therefore has no access to time. Being imported by a module that does have access to time does not confer to the imported module that access.
Is it a good idea to use a standard library function from an imported module? For example, I write a xyz.py module and within xyz.py, I've this statetment import json
I have another script where I import xyz. In this script I need to make use of json functions. I can for sure import json in my script but json lib was already imported when I import xyz. So can I use xyz.json() or is it a bad practice?
You should use import json again to explicitly declare the dependency.
Python will optimize the way it loads the modules so you don't have to be concerned with inefficiency.
If you later don't need xyz.py anymore and you drop that import, then you still want import json to be there without having to re-analyze your dependencies.
The code:
from os import path
path.__dict__['os'].system("/bin/sh")
Allows me to make a shell in python. I am curious why the os module can be accessed through the path class, when I didn't explicitly import the entire os module. I have read a few articles on dict, and how it stores the variables, methods, to the class etc. But I didn't find that it would keep the module it came from.
It doesn't have anything special to do with __dict__; you can also get it as just path.os. The os.path module imports the os module. That means that the name os is accessible from os.path. Anytime a module does import foo, you can access foo via that module just like you'd access anything else in the module. Modules are just normal objects, and imported modules are accessible just like classes or functions or anything else in a module.
When is it useful to use imp.load_source() method for importing Python module? Has it some advantage in some scenario in opposite to normal importing with import keyword?
import always looks in the following order:
already imported modules
import hooks
files in the locations in sys.path
builtin modules
If you want to import a module which would not be found by any of these mechanisms, but you know the filename, then you could use imp.load_source(). Or if you want to import a module that would be shadowed by an earlier import mechanism, for example if you want to import foo from a directory in sys.path but there is a custom import hook that would find its own version of foo first, then you could use imp.load_source() for that too. Basically it lets you control the source of the module's code in a way that import does not.