I would like to know if it is possible to import some variables from another python file using importlib.import_module function (or another similar). I need to use importlib because in my project I employ a variable for the name of the file. For instance, if the name of the file was explicitly given - let this be myfile - I would use
from myfile import a, b
to import variables a and b.
But for the case of myfile being a variable for the file name, I was thinking that I could use something like
import importlib
a = importlib.import_module(myfile.a)
However this seems to only work for the case of myfile being a variable for the name of a package and not a variable for the name of a file. If it is the case of the latter and the name of the file is for instance "foo", the error
No module named 'foo.a'; 'foo' is not a package
happens. Also, I did not find a way to import the additional variable b through the importlib.import_module function. Is there any importlib function that could do this?
We ended up using something like
imported_function = getattr(import_module(module_name), function_name)
Related
I want to import some package depending on which value the user chooses.
The default is file1.py:
from files import file1
If user chooses file2, it should be :
from files import file2
In PHP, I can do this using variable variables:
$file_name = 'file1';
include($$file_name);
$file_name = 'file2';
include($$file_name);
How can I do this in Python?
Python doesn't have a feature that's directly equivalent to PHP's "variable variables". To get a "variable variable"'s value (or the value of any other expression) you can use the eval function.
foo = "Hello World"
print eval("foo")
However, this can't be used in an import statement.
It is possible to use the __import__ function to import using a variable.
package = "os"
name = "path"
imported = getattr(__import__(package, fromlist=[name]), name)
is equivalent to
from os import path as imported
Old thread, but I needed the answer, so someone else still might...
There's a cleaner way to do this in Python 2.7+:
import importlib
my_module = importlib.import_module("package.path.%s" % module_name)
As Fredrik Lundh states:
Anyway, here’s how these statements and functions work:
import X imports the module X, and creates a reference to that module
in the current namespace. Or in other words, after you’ve run this
statement, you can use X.name to refer to things defined in module X.
from X import * imports the module X, and creates references in the
current namespace to all public objects defined by that module (that
is, everything that doesn’t have a name starting with “_”). Or in
other words, after you’ve run this statement, you can simply use a
plain name to refer to things defined in module X. But X itself is not
defined, so X.name doesn’t work. And if name was already defined, it
is replaced by the new version. And if name in X is changed to point
to some other object, your module won’t notice.
from X import a, b, c imports the module X, and creates references in
the current namespace to the given objects. Or in other words, you can
now use a and b and c in your program.
Finally, X = __import__(‘X’) works like import X, with the difference
that you 1) pass the module name as a string, and 2) explicitly assign
it to a variable in your current namespace.
And by the way that's the last one method that you're intrested in.
Simply write (for example):
var = "datetime"
module = __import__(var)
Basing myself on mattjbray's answer:
from importlib import import_module
# lookup in a set is in constant time
safe_names = {"file1.py", "file2.py", "file3.py", ...}
user_input = ...
if user_input in safe_names:
file = import_module(user_input)
else:
print("Nope, not doing this.")
Saves a few lines of code, and allows you to set safe_names programmatically, or load multiple modules and assign them to a dict, for example.
It's probably a very bad idea to let the user choose what to import. Packages can execute code on import, so you're effectively allowing a user to arbitrarily execute code on your system! Much safer to do something like
if user_input == 'file1.py':
from files import file1 as file
elif user_input == 'file2.py':
from files import file2 as file
else:
file = None
print "Sorry, you can't import that file"
I am in the habit of using raw_input(...) for certain debugging. However, in python3 this has changed to input(...). Is there a way to define an alias at the top of my project, such as:
# __init__.py
raw_input = input
I tried the above, but it only worked in the file I added it to, and not any other files in that directory. I'd like this to work basically in every file within my python repository.
You can define all aliases in a separate file (e.g. aliases.py) then import said file where needed (i.e. import aliases).
The con with this method that you'll be referencing the alias through aliases.alias unless you make the import stricter (i.e. from aliases import raw_input) or if you don't care about avoiding a wildcard import (i.e. from aliases import *).
Additionally, if you don't mind another import in the aliases file you can use the builtins namespace:
import builtins
builtins.raw_input = input
You still have to define all aliases separate file (e.g. aliases.py) then import said file where needed (i.e. import aliases) but the advantage of using the builtins namespace is that you can use that import exactly as given.
You can do it by creating a module for creating the renaming function and then importing it to every file you want to like this:
First the module function declaration in alias.py
def raw_input(a):
return input(a)
Secondly, import to another file:
from alias import raw_input
x = raw_input("hello world")
print(x)
Sadly, you will have to make the import of the module to every file you want to use the renamed function.
Hope it works for you!
Put this at the top, and you will get exactly what you want.
import builtins
builtins.raw_input = builtins.input
It is guaranteed to work, but generally considered a bad practice (everybody will be confused with where is that raw_input defined)
I have a .py file containing some functions. One of the functions requires Python's csv module. Lets call it foo.
Here is the thing: if I enter the python shell, import the csv module, write the defitinion of foo and use it, everything runs fine.
The problem comes when I try to import foo from a custom module. If I enter the python shell, import the csv module, import the module where foo is located and try to use it, it will returns an error stating that 'csv' has not been defined (it behaves as if the csv module had not been imported).
I'm wondering if I'm missing some kind of scope behaviour related to imports.
How can I enable foo to use the csv module or any other module it requires?
Thank you in advance
By importing it in the file that defines the foo function.
The foo function doesn't know to look in the dictionary containing the globals you use in the REPL (where you have imported csv). It looks in the globals of it's module (there's other steps here of course), if it doesn't find it there you'll get a NameError.
I want to import some package depending on which value the user chooses.
The default is file1.py:
from files import file1
If user chooses file2, it should be :
from files import file2
In PHP, I can do this using variable variables:
$file_name = 'file1';
include($$file_name);
$file_name = 'file2';
include($$file_name);
How can I do this in Python?
Python doesn't have a feature that's directly equivalent to PHP's "variable variables". To get a "variable variable"'s value (or the value of any other expression) you can use the eval function.
foo = "Hello World"
print eval("foo")
However, this can't be used in an import statement.
It is possible to use the __import__ function to import using a variable.
package = "os"
name = "path"
imported = getattr(__import__(package, fromlist=[name]), name)
is equivalent to
from os import path as imported
Old thread, but I needed the answer, so someone else still might...
There's a cleaner way to do this in Python 2.7+:
import importlib
my_module = importlib.import_module("package.path.%s" % module_name)
As Fredrik Lundh states:
Anyway, here’s how these statements and functions work:
import X imports the module X, and creates a reference to that module
in the current namespace. Or in other words, after you’ve run this
statement, you can use X.name to refer to things defined in module X.
from X import * imports the module X, and creates references in the
current namespace to all public objects defined by that module (that
is, everything that doesn’t have a name starting with “_”). Or in
other words, after you’ve run this statement, you can simply use a
plain name to refer to things defined in module X. But X itself is not
defined, so X.name doesn’t work. And if name was already defined, it
is replaced by the new version. And if name in X is changed to point
to some other object, your module won’t notice.
from X import a, b, c imports the module X, and creates references in
the current namespace to the given objects. Or in other words, you can
now use a and b and c in your program.
Finally, X = __import__(‘X’) works like import X, with the difference
that you 1) pass the module name as a string, and 2) explicitly assign
it to a variable in your current namespace.
And by the way that's the last one method that you're intrested in.
Simply write (for example):
var = "datetime"
module = __import__(var)
Basing myself on mattjbray's answer:
from importlib import import_module
# lookup in a set is in constant time
safe_names = {"file1.py", "file2.py", "file3.py", ...}
user_input = ...
if user_input in safe_names:
file = import_module(user_input)
else:
print("Nope, not doing this.")
Saves a few lines of code, and allows you to set safe_names programmatically, or load multiple modules and assign them to a dict, for example.
It's probably a very bad idea to let the user choose what to import. Packages can execute code on import, so you're effectively allowing a user to arbitrarily execute code on your system! Much safer to do something like
if user_input == 'file1.py':
from files import file1 as file
elif user_input == 'file2.py':
from files import file2 as file
else:
file = None
print "Sorry, you can't import that file"
I would like to load a .py file at runtime. This .py file is basically a config file with the following format:
var1=value
var2=value
predicate_function=func line : <return true or false>
Once this file is loaded, I would like to be able to access var1, var2 and predicate_function. For each line, I'll pass it to the predicate function, and if it returns false, I'll ignore it.
In any case, I'm not sure how to load a python file at runtime and access its variables.
Clarification: there may be any number of these config files that I need to pass to the main program and I won't know their names until runtime. Google tells me I should use __import__. I'm not sure how to correctly use that method and then access the variables of the imported file.
As written in the python official documentation, if you just want to import a module by name, you can look it up in the sys.modules dictionary after using __import__.
Supposing your configuration is in myproject.mymodule, you would do like that :
module_name = 'myproject.mymodule'
import sys
__import__(module_name)
mymodule = sys.modules[module_name]
# Then you can just access your variables and functions
print mymodule.var1
print mymodule.var2
# etc...
You can also use the return value of __import__ statement but you will have to understand fully how python works with namespaces and scopes.
You just need to be able to dynamically specify the imports and then dynamically get at the variables.
Let's say your config file is bar.py and looks like this:
x = 3
y = 4
def f(x): return (x<4)
Then your code should look like this:
import sys
# somehow modnames should be a list of strings that are the names of config files
#
# you can do this more dynamically depending on what you're doing
modnames = ['bar']
for modname in modnames:
exec('import %s' % modname)
for modname in modnames:
mod = sys.modules[modname]
for k in mod.__dict__:
if k[:2] != '__':
print modname, k, mod.__dict__[k]
I get this output:
bar f <function f at 0x7f2354eb4cf8>
bar x 3
bar y 4
Then you at least have all the variables and functions. I didn't quite get what you wanted from the predicate functions, but maybe you can get that on your own now.
To access another Python module, you import it. execfile has been mentioned by a couple people, but it is messy and dangerous. execfile clutters your namespace, possibly even messing up the code you are running. When you want to access another Python source file, use the import statement.
Even better would be not to use a Python file for configuration at all, but rather to use the builtin module ConfigParser or a serialization format like JSON. This way your configuration files don't allow execution of arbitrary (possibly malicious) code, doesn't require people to know Python to configure your program, and can easily be altered programatically.
If the imported module is on the regular search path, you can use __import__.
If you need to load the module from an arbitrary path in the filesystem, use imp.load_module.
Be sure to consider the security implications of loading arbitrary user-specified code.
In Python 2.*, execfile works (I recommend passing a specific dictionary and accessing the variables from there -- as the note in the docs says, execfile can't affect the calling function's locals() dictionary).
In Python 3.*, execfile has been removed, so do, instead:
with open('thefile.py') as f:
exec(f.read(), somedict)
Since the Python version hasn't been clearly mentioned, it is worth pointing out that the imp module has been deprecated in newer Python versions in favor of the importlib module. Example here.
I'm kinda late to the party, but I want to present an alternative answer nonetheless.
If you want to import code without affecting the global module namespace, you can create an anonymous module (using types.ModuleType) and load arbitrary code in it (using compile and exec). For instance, like this:
import types
filename = "/path/to/your/file.py"
with open(filename) as fp:
code = compile(fp.read(), filename, "exec")
config_module = types.ModuleType("<config>")
exec code in config_module.__dict__
You can then access the variables as config_module.var1, &c.
If you want to have a configuration file that will only be edited by the user when the program isn't running, just import it as a normal python file
ie.
main.py:
import config
print config.var1
config.py:
var="var12"
var2 = 100.5
try the imp module : http://docs.python.org/library/imp.html