I'm trying to use a third-party lib (docutils) on Google App Engine and have a problem with this code (in docutils):
try:
import pwd
do stuff
except ImportError:
do other stuff
I want the import to fail, as it will on the actual GAE server, but the problem is that it doesn't fail on my development box (ubuntu). How to make it fail, given that the import is not in my own code?
Even easier than messing with __import__ is just inserting None in the sys.modules dict:
>>> import sys
>>> sys.modules['pwd'] = None
>>> import pwd
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ImportError: No module named pwd
In your testing framework, before you cause docutils to be imported, you can perform this setup task:
import __builtin__
self.savimport = __builtin__.__import__
def myimport(name, *a):
if name=='pwd': raise ImportError
return self.savimport(name, *a)
__builtin__.__import__ = myimport
and of course in teardown put things back to normal:
__builtin__.__import__ = self.savimport
Explanation: all import operations go through __builtin__.__import__, and you can reassign that name to have such operations use your own code (alternatives such as import hooks are better for such purposes as performing import from non-filesystem sources, but for purposes such as yours, overriding __builtin__.__import__, as you see above, affords truly simple code).
I'm trying to import the requests module to get familiar with bs4, but the request module in the file I'm currently working in is grayed out so it isn't being recognized as a module. When I run the almost empty program, I get an error for an unrelated python file within my project.
Should I individually store each python file I make inside of a separate folder?
Both of these files are inside of the same project folder.
import requests
response = get('https://www.newegg.ca/p/N82E16868105274')
print(response.raise_for_status())
Error:
Traceback (most recent call last):
File "C:\Users\Denze\MyPythonScripts\Webscraping learning\beautifulsoup tests.py", line 1, in <module>
import requests
File "C:\Users\Denze\MyPythonScripts\requests.py", line 3, in <module>
res = requests.get('')
AttributeError: partially initialized module 'requests' has no attribute 'get' (most likely due to a circular import)
Process finished with exit code 1
The other code in question that I think is causing my error:
import requests
res = requests.get('')
playFile = ('TestDownload.txt', 'wb')
for chunk in res.iter_content(100000):
playFile.write(chunk)
playFile.close()
You have a name collision. You're not importing the requests library, you're importing your script.
You wanted to do the following with your imports:
MyPythonScripts\beautifulsoup tests.py
→ requests.get() (the library)
What you're doing instead is:
MyPythonScripts\beautifulsoup tests.py
→ MyPythonScripts\requests.py
→ MyPythonScripts\requests.py .get() (the same file again)
That's the "circular import" that is mentioned in the traceback. The module imports itself and tries to use an attribute that isn't there before it finishes "executing", so the interpreter thinks it's due to the unfinished initialization
Raname MyPythonScripts\requests.py to something else and it should work.
I would like to narrow the common error "attempted relative import beyond top-level package" down by including the exception-handling in the imports already.
In my Django tests in DjangoProject/tests.py I wrote the imports relative to itself (tests.py).
The default unittests.py which executes each testfile is located in the root-folder which also includes the DjangoProject-folder.
As I was getting the error attempted relative import beyond top-level package the moment I added the
DjangoProject/tests.py to my Unit-Tests adnd it was clear it came from the imports. With a try/except I was able to write a slightly clearer error so I'm not in the need of guessing around why and which file caused the error.
Now my code looks like this:
try:
from django.utils.safestring import mark_safe
import json
from django.conf import settings
from viewsfunctions import *
from .. import PoM
import unittest
except Exception as importex:
print("Error in the tests.py-imports: "+str(importex))
And it threw first of all the message:
"No module named 'viewsfunctions'"
which makes sense and is helpful as viewsfunctions is a module inside DjangoProject. I replaced the line with: from DjangoProject.viewsfunctions import *
The next error is:
Error in the Imports: attempted relative import beyond top-level package
And this is exactly my problem. This could be anything. By just pdbing around I could track it down to from .. import PoM (as the module PoM is relative to tests.py in the top-folder, but relative to the executing unittests.py in the same folder)
In this case with just a few imports it's relatively fast to narrow it down, but is there any way to write a better exception message or deliver somehow more information in which of the import-lines the error actually happened?
If you would simply not catch the exception, you'd get a very useful traceback:
>>> from .. import foo
Traceback (most recent call last):
File "<input>", line 1, in <module>
File "/Users/deceze/...", line 21, in do_import
module = self._system_import(name, *args, **kwargs)
ImportError: attempted relative import with no known parent package
The problem is that you're catching the exception and are only printing the most minimal error message possible. If you do want to catch the exception for some reason yet still get a complete error message, the easiest way would be to use the logging module:
import logging
try:
...
except:
logging.exception('Error fooing the bar')
This will produce your custom error message followed by a complete stack trace.
To get even more manual, use the traceback module:
import traceback
try:
...
except:
print('Error fooing the bar')
traceback.print_exc()
With other functions in traceback you can get even more granular and print or retrieve messages from an exception as granular as you like.
How can I know if a Python module exists, without importing it?
Importing something that might not exist (not what I want) results in:
try:
import eggs
except ImportError:
pass
TL;DR) Use importlib.util.find_spec(module_name) (Python 3.4+).
Python2: imp.find_module
To check if import can find something in Python 2, using imp:
import imp
try:
imp.find_module('eggs')
found = True
except ImportError:
found = False
To find dotted imports, you need to do more:
import imp
try:
spam_info = imp.find_module('spam')
spam = imp.load_module('spam', *spam_info)
imp.find_module('eggs', spam.__path__) # __path__ is already a list
found = True
except ImportError:
found = False
You can also use pkgutil.find_loader (more or less the same as the Python 3 part:
import pkgutil
eggs_loader = pkgutil.find_loader('eggs')
found = eggs_loader is not None
Python 3
Python 3 ≤ 3.3: importlib.find_loader
You should use importlib. I went about doing this like:
import importlib
spam_loader = importlib.find_loader('spam')
found = spam_loader is not None
My expectation being, if you can find a loader for it, then it exists. You can also be a bit more smart about it, like filtering out what loaders you will accept. For example:
import importlib
spam_loader = importlib.find_loader('spam')
# only accept it as valid if there is a source file for the module - no bytecode only.
found = issubclass(type(spam_loader), importlib.machinery.SourceFileLoader)
Python 3 ≥ 3.4: importlib.util.find_spec
In Python 3.4 importlib.find_loader Python documentation was deprecated in favour of importlib.util.find_spec. The recommended method is the importlib.util.find_spec. There are others like importlib.machinery.FileFinder, which is useful if you're after a specific file to load. Figuring out how to use them is beyond the scope of this.
import importlib
spam_spec = importlib.util.find_spec("spam")
found = spam_spec is not None
This also works with relative imports, but you must supply the starting package, so you could also do:
import importlib
spam_spec = importlib.util.find_spec("..spam", package="eggs.bar")
found = spam_spec is not None
spam_spec.name == "eggs.spam"
While I'm sure there exists a reason for doing this - I'm not sure what it would be.
Warning
When trying to find a submodule, it will import the parent module (for ALL of the above methods)!
food/
|- __init__.py
|- eggs.py
## __init__.py
print("module food loaded")
## eggs.py
print("module eggs")
were you then to run
>>> import importlib
>>> spam_spec = importlib.util.find_spec("food.eggs")
module food loaded
ModuleSpec(name='food.eggs', loader=<_frozen_importlib.SourceFileLoader object at 0x10221df28>, origin='/home/user/food/eggs.py')
Comments are welcome on getting around this
Acknowledgements
#rvighne for importlib
#lucas-guido for Python 3.3+ deprecating find_loader
#enpenax for pkgutils.find_loader behaviour in Python 2.7
Python 3 >= 3.6: ModuleNotFoundError
The ModuleNotFoundError has been introduced in Python 3.6 and can be used for this purpose:
try:
import eggs
except ModuleNotFoundError:
# Error handling
pass
The error is raised when a module or one of its parents cannot be found. So
try:
import eggs.sub
except ModuleNotFoundError as err:
# Error handling
print(err)
would print a message that looks like No module named 'eggs' if the eggs module cannot be found; but it would print something like No module named 'eggs.sub' if only the sub module couldn't be found, but the eggs package could be found.
See the documentation of the import system for more information on the ModuleNotFoundError.
After using yarbelk's response, I've made this so I don't have to import ìmp.
try:
__import__('imp').find_module('eggs')
# Make things with a supposed existing module
except ImportError:
pass
It is useful in Django's settings.py file, for example.
Python 2, without relying on ImportError
Until the current answer is updated, here is the way for Python 2
import pkgutil
import importlib
if pkgutil.find_loader(mod) is not None:
return importlib.import_module(mod)
return None
Why another answer?
A lot of answers make use of catching an ImportError. The problem with that is, that we cannot know what throws the ImportError.
If you import your existent module and there happens to be an ImportError in your module (e.g., typo on line 1), the result will be that your module does not exist.
It will take you quite the amount of backtracking to figure out that your module exists and the ImportError is caught and makes things fail silently.
go_as's answer as a one-liner:
python -c "help('modules');" | grep module
Use one of the functions from pkgutil, for example:
from pkgutil import iter_modules
def module_exists(module_name):
return module_name in (name for loader, name, ispkg in iter_modules())
I wrote this helper function:
def is_module_available(module_name):
if sys.version_info < (3, 0):
# python 2
import importlib
torch_loader = importlib.find_loader(module_name)
elif sys.version_info <= (3, 3):
# python 3.0 to 3.3
import pkgutil
torch_loader = pkgutil.find_loader(module_name)
elif sys.version_info >= (3, 4):
# python 3.4 and above
import importlib
torch_loader = importlib.util.find_spec(module_name)
return torch_loader is not None
Here is a way to check if a module is loaded from the command line:
Linux/UNIX script file method: make a file module_help.py:
#!/usr/bin/env python
help('modules')
Then make sure it's executable: chmod u+x module_help.py
And call it with a pipe to grep:
./module_help.py | grep module_name
Invoke the built-in help system. (This function is intended for interactive use.) If no argument is given, the interactive help system starts on the interpreter console. If the argument is a string, then the string is looked up as the name of a module, function, class, method, keyword, or documentation topic, and a help page is printed on the console. If the argument is any other kind of object, a help page on the object is generated.
Interactive method: in the console, load python
>>> help('module_name')
If found, quit reading by typing q.
To exit the Python interpreter interactive session, press Ctrl + D
Windows script file method, also Linux/UNIX compatible, and better overall:
#!/usr/bin/env python
import sys
help(sys.argv[1])
Calling it from the command like:
python module_help.py site
Would output:
Help on module site:
NAME
site - Append module search paths for third-party packages to sys.path.
FILE
/usr/lib/python2.7/site.py
MODULE DOCS
http://docs.python.org/library/site
DESCRIPTION
...
:
And you'd have to press q to exit interactive mode.
Using it for an unknown module, e.g.,
python module_help.py lkajshdflkahsodf
Would output:
no Python documentation found for 'lkajshdflkahsodf'
and exit.
You could just write a little script that would try to import all the modules and tell you which ones are failing and which ones are working:
import pip
if __name__ == '__main__':
for package in pip.get_installed_distributions():
pack_string = str(package).split(" ")[0]
try:
if __import__(pack_string.lower()):
print(pack_string + " loaded successfully")
except Exception as e:
print(pack_string + " failed with error code: {}".format(e))
Output:
zope.interface loaded successfully
zope.deprecation loaded successfully
yarg loaded successfully
xlrd loaded successfully
WMI loaded successfully
Werkzeug loaded successfully
WebOb loaded successfully
virtualenv loaded successfully
...
A word of warning: this will try to import everything, so you'll see things like PyYAML failed with error code: No module named pyyaml, because the actual import name is just yaml. So as long as you know your imports, this should do the trick for you.
There isn't any way to reliably check if "dotted module" is importable without importing its parent package. Saying this, there are many solutions to problem "how to check if a Python module exists".
The below solution addresses the problem that an imported module can raise an ImportError even if it exists. We want to distinguish that situation from such in which the module does not exist.
Python 2:
import importlib
import pkgutil
import sys
def find_module(full_module_name):
"""
Returns module object if module `full_module_name` can be imported.
Returns None if module does not exist.
Exception is raised if (existing) module raises exception during its import.
"""
module = sys.modules.get(full_module_name)
if module is None:
module_path_tail = full_module_name.split('.')
module_path_head = []
loader = True
while module_path_tail and loader:
module_path_head.append(module_path_tail.pop(0))
module_name = ".".join(module_path_head)
loader = bool(pkgutil.find_loader(module_name))
if not loader:
# Double check if module realy does not exist
# (case: full_module_name == 'paste.deploy')
try:
importlib.import_module(module_name)
except ImportError:
pass
else:
loader = True
if loader:
module = importlib.import_module(full_module_name)
return module
Python 3:
import importlib
def find_module(full_module_name):
"""
Returns module object if module `full_module_name` can be imported.
Returns None if module does not exist.
Exception is raised if (existing) module raises exception during its import.
"""
try:
return importlib.import_module(full_module_name)
except ImportError as exc:
if not (full_module_name + '.').startswith(exc.name + '.'):
raise
In django.utils.module_loading.module_has_submodule:
import sys
import os
import imp
def module_has_submodule(package, module_name):
"""
check module in package
django.utils.module_loading.module_has_submodule
"""
name = ".".join([package.__name__, module_name])
try:
# None indicates a cached miss; see mark_miss() in Python/import.c.
return sys.modules[name] is not None
except KeyError:
pass
try:
package_path = package.__path__ # No __path__, then not a package.
except AttributeError:
# Since the remainder of this function assumes that we're dealing with
# a package (module with a __path__), so if it's not, then bail here.
return False
for finder in sys.meta_path:
if finder.find_module(name, package_path):
return True
for entry in package_path:
try:
# Try the cached finder.
finder = sys.path_importer_cache[entry]
if finder is None:
# Implicit import machinery should be used.
try:
file_, _, _ = imp.find_module(module_name, [entry])
if file_:
file_.close()
return True
except ImportError:
continue
# Else see if the finder knows of a loader.
elif finder.find_module(name):
return True
else:
continue
except KeyError:
# No cached finder, so try and make one.
for hook in sys.path_hooks:
try:
finder = hook(entry)
# XXX Could cache in sys.path_importer_cache
if finder.find_module(name):
return True
else:
# Once a finder is found, stop the search.
break
except ImportError:
# Continue the search for a finder.
continue
else:
# No finder found.
# Try the implicit import machinery if searching a directory.
if os.path.isdir(entry):
try:
file_, _, _ = imp.find_module(module_name, [entry])
if file_:
file_.close()
return True
except ImportError:
pass
# XXX Could insert None or NullImporter
else:
# Exhausted the search, so the module cannot be found.
return False
In case you know the location of file and want to check that the respective Python code file has that module or not, you can simply check via the astor package in Python. Here is a quick example:
"""
Check if a module function exists or not without importing a Python package file
"""
import ast
import astor
tree = astor.parse_file('handler.py')
method_to_check = 'handle'
for item in tree.body:
if isinstance(item, ast.FunctionDef):
if item.name == method_to_check:
print('method exists')
break
A simpler if statement from Ask Ubuntu, How do I check whether a module is installed in Python?:
import sys
print('eggs' in sys.modules)
You can also use importlib.util directly
import importlib.util
def module_exists_without_import(module_name):
spec = importlib.util.find_spec(module_name)
return spec is not None
I have a module called spellnum. It can be used as a command-line utility (it has the if __name__ == '__main__': block) or it can be imported like a standard Python module.
The module defines a class named Speller which looks like this:
class Speller(object):
def __init__(self, lang="en"):
module = __import__("spelling_" + lang)
# use module's contents...
As you can see, the class constructor loads other modules at runtime. Those modules (spelling_en.py, spelling_es.py, etc.) are located in the same directory as the spellnum.py itself.
Besides spellnum.py, there are other files with utility functions and classes. I'd like to hide those files since I don't want to expose them to the user and since it's a bad idea to pollute the Python's lib directory with random files. The only way to achieve this that I know of is to create a package.
I've come up with this layout for the project (inspired by this great tutorial):
spellnum/ # project root
spellnum/ # package root
__init__.py
spellnum.py
spelling_en.py
spelling_es.py
squash.py
# ... some other private files
test/
test_spellnum.py
example.py
The file __init__.py contains a single line:
from spellnum import Speller
Given this new layout, the code for dynamic module loading had to be changed:
class Speller(object):
def __init__(self, lang="en"):
spelling_mod = "spelling_" + lang
package = __import__("spellnum", fromlist=[spelling_mod])
module = getattr(package, spelling_mod)
# use module as usual
So, with this project layout a can do the following:
Successfully import spellnum inside example.py and use it like a simple module:
# an excerpt from the example.py file
import spellnum
speller = spellnum.Speller(es)
# ...
import spellnum in the tests and run those tests from the project root like this:
$ PYTHONPATH="`pwd`:$PYTHONPATH" python test/test_spellnum.py
The problem
I cannot execute spellnum.py directly with the new layout. When I try to, it shows the following error:
Traceback (most recent call last):
...
File "spellnum/spellnum.py", line 23, in __init__
module = getattr(package, spelling_mod)
AttributeError: 'module' object has no attribute 'spelling_en'
The question
What's the best way to organize all of the files required by my module to work so that users are able to use the module both from command line and from their Python code?
Thanks!
How about keeping spellnum.py?
spellnum.py
spelling/
__init__.py
en.py
es.py
Your problem is, that the package is called the same as the python-file you want to execute, thus importing
from spellnum import spellnum_en
will try to import from the file instead of the package. You could fiddle around with relative imports, but I don't know how to make them work with __import__, so I'd suggest the following:
def __init__(self, lang="en"):
mod = "spellnum_" + lang
module = None
if __name__ == '__main__':
module = __import__(mod)
else:
package = getattr(__import__("spellnum", fromlist=[mod]), mod)