我如何知道Python模块是否存在,而不导入它?
导入一些可能不存在(不是我想要的)的东西会导致:
try:
import eggs
except ImportError:
pass
我如何知道Python模块是否存在,而不导入它?
导入一些可能不存在(不是我想要的)的东西会导致:
try:
import eggs
except ImportError:
pass
当前回答
Go_as的回答是一行:
python -c "help('modules');" | grep module
其他回答
你可以写一个小脚本,尝试导入所有的模块,并告诉你哪些是失败的,哪些是工作的:
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))
输出:
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
...
警告一句:这将尝试导入所有内容,因此您将看到类似PyYAML失败的错误代码:没有名为PyYAML的模块,因为实际的导入名称只是yaml。只要知道导入,这个就能帮到你。
Ask Ubuntu的一个更简单的if语句,如何检查Python中是否安装了一个模块?:
import sys
print('eggs' in sys.modules)
如果你知道文件的位置,想要检查相应的Python代码文件是否有该模块,你可以简单地通过Python中的astor包进行检查。这里有一个简单的例子:
"""
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
在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
Python 3 >= 3.6: ModuleNotFoundError
ModuleNotFoundError已在Python 3.6中引入,可用于以下目的:
try:
import eggs
except ModuleNotFoundError:
# Error handling
pass
当无法找到模块或其父模块之一时,将引发此错误。所以
try:
import eggs.sub
except ModuleNotFoundError as err:
# Error handling
print(err)
如果找不到eggs模块,将打印类似于No module named 'eggs'的消息;但它会打印类似于没有名为“eggs”的模块。如果子模块找不到,但鸡蛋包可以找到,则Sub '。
有关ModuleNotFoundError的更多信息,请参阅导入系统的文档。