Import a package in python
Python PackageIn this article, you'll learn to divide your code base into clean, efficient modules using Python packages. Also, you'll learn to import and use your own or third party packages in a Python program. Show
Video: Python Packages: Organize Your Code
What are packages?We don't usually store all of our files on our computer in the same location. We use a well-organized hierarchy of directories for easier access. Similar files are kept in the same directory, for example, we may keep all the songs in the "music" directory. Analogous to this, Python has packages for directories and modules for files. As our application program grows larger in size with a lot of modules, we place similar modules in one package and different modules in different packages. This makes a project (program) easy to manage and conceptually clear. Similarly, as a directory can contain subdirectories and files, a Python package can have sub-packages and modules. A directory must contain a file named Here is an example. Suppose we are developing a game. One possible organization of packages and modules could be as shown in the figure below. Package Module Structure in Python ProgrammingImporting module from a packageWe can import modules from packages using the dot (.) operator. For example, if we want to import the
Now, if this module contains a function named
If this construct seems lengthy, we can import the module without the package prefix as follows:
We can now call the function simply as follows:
Another way of importing just the required function (or class or variable) from a module within a package would be as follows:
Now we can directly call this function.
Although easier, this method is not recommended. Using the full namespace avoids confusion and prevents two same identifier names from colliding. While importing packages, Python looks in the list of directories defined in
If you quit from the Python interpreter and enter it again, the definitions you have made (functions and variables) are lost. Therefore, if you want to write a somewhat longer program, you are better off using a text editor to prepare the input for the interpreter and running it with that file as input instead. This is known as creating a script. As your program gets longer, you may want to split it into several files for easier maintenance. You may also want to use a handy function that you’ve written in several programs without copying its definition into each program. To support this, Python has a way to put definitions in a file and use them in a script or in an interactive instance of the interpreter. Such a file is called a module; definitions from a module can be imported into other modules or into the main module (the collection of variables that you have access to in a script executed at the top level and in calculator mode). A module is a file containing Python definitions and statements. The file name is the module name with the suffix # Fibonacci numbers module def fib(n): # write Fibonacci series up to n a, b = 0, 1 while a < n: print(a, end=' ') a, b = b, a+b print() def fib2(n): # return Fibonacci series up to n result = [] a, b = 0, 1 while a < n: result.append(a) a, b = b, a+b return result Now enter the Python interpreter and import this module with the following command: This does not add the names of the functions defined in >>> fibo.fib(1000) 0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 >>> fibo.fib2(100) [0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89] >>> fibo.__name__ 'fibo' If you intend to use a function often you can assign it to a local name: >>> fib = fibo.fib >>> fib(500) 0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 6.1. More on Modules¶A module can contain executable statements as well as function definitions. These statements are intended to initialize the module. They are executed only the first time the module name is encountered in an import statement. 1 (They are also run if the file is executed as a script.) Each module has its own private namespace, which is used as the global namespace by all functions defined in the module. Thus, the author of a module can use global variables in the module without worrying about accidental clashes with a
user’s global variables. On the other hand, if you know what you are doing you can touch a module’s global variables with the same notation used to refer to its functions, Modules can import other modules. It is customary but not required to place all There is a variant of the >>> from fibo import fib, fib2 >>> fib(500) 0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 This does not introduce the module name from which the imports are taken in the local namespace (so in the example, There is even a variant to import all names that a module defines: >>> from fibo import * >>> fib(500) 0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 This imports all names except those beginning with an underscore ( Note that in general the practice of importing If the module name is followed by >>> import fibo as fib >>> fib.fib(500) 0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 This is effectively importing the module in the same way that It can also be used when utilising >>> from fibo import fib as fibonacci >>> fibonacci(500) 0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 Note For efficiency reasons, each module is only imported once per interpreter session. Therefore, if you change your modules, you must restart the interpreter – or, if it’s just one module you want to test interactively, use 6.1.1. Executing modules as scripts¶When you run a Python module with python fibo.py <arguments> the code in the module will be executed, just as if you imported it, but with the if __name__ == "__main__": import sys fib(int(sys.argv[1])) you can make the file usable as a script as well as an importable module, because the code that parses the command line only runs if the module is executed as the “main” file: $ python fibo.py 50 0 1 1 2 3 5 8 13 21 34 If the module is imported, the code is not run: This is often used either to provide a convenient user interface to a module, or for testing purposes (running the module as a script executes a test suite). 6.1.2. The Module Search Path¶When a module named
Note On file systems which support symlinks, the directory containing the input script is calculated after the symlink is followed. In other words the directory containing the symlink is not added to the module search path. After initialization, Python
programs can modify 6.1.3. “Compiled” Python files¶To speed up loading modules, Python caches the compiled version of each module in the Python checks the modification date of the source against the compiled version to see if it’s out of date and needs to be recompiled. This is a completely automatic process. Also, the compiled modules are platform-independent, so the same library can be shared among systems with different architectures. Python does not check the cache in two circumstances. First, it always recompiles and does not store the result for the module that’s loaded directly from the command line. Second, it does not check the cache if there is no source module. To support a non-source (compiled only) distribution, the compiled module must be in the source directory, and there must not be a source module. Some tips for experts:
6.2. Standard Modules¶Python comes with a library of standard modules, described in a separate document, the Python Library Reference (“Library Reference” hereafter). Some modules are built into the interpreter; these provide access to operations that
are not part of the core of the language but are nevertheless built in, either for efficiency or to provide access to operating system primitives such as system calls. The set of such modules is a configuration option which also depends on the underlying platform. For example, the >>> import sys >>> sys.ps1 '>>> ' >>> sys.ps2 '... ' >>> sys.ps1 = 'C> ' C> print('Yuck!') Yuck! C> These two variables are only defined if the interpreter is in interactive mode. The variable >>> import sys >>> sys.path.append('/ufs/guido/lib/python') 6.3. The dir() Function¶The built-in function >>> import fibo, sys >>> dir(fibo) ['__name__', 'fib', 'fib2'] >>> dir(sys) ['__breakpointhook__', '__displayhook__', '__doc__', '__excepthook__', '__interactivehook__', '__loader__', '__name__', '__package__', '__spec__', '__stderr__', '__stdin__', '__stdout__', '__unraisablehook__', '_clear_type_cache', '_current_frames', '_debugmallocstats', '_framework', '_getframe', '_git', '_home', '_xoptions', 'abiflags', 'addaudithook', 'api_version', 'argv', 'audit', 'base_exec_prefix', 'base_prefix', 'breakpointhook', 'builtin_module_names', 'byteorder', 'call_tracing', 'callstats', 'copyright', 'displayhook', 'dont_write_bytecode', 'exc_info', 'excepthook', 'exec_prefix', 'executable', 'exit', 'flags', 'float_info', 'float_repr_style', 'get_asyncgen_hooks', 'get_coroutine_origin_tracking_depth', 'getallocatedblocks', 'getdefaultencoding', 'getdlopenflags', 'getfilesystemencodeerrors', 'getfilesystemencoding', 'getprofile', 'getrecursionlimit', 'getrefcount', 'getsizeof', 'getswitchinterval', 'gettrace', 'hash_info', 'hexversion', 'implementation', 'int_info', 'intern', 'is_finalizing', 'last_traceback', 'last_type', 'last_value', 'maxsize', 'maxunicode', 'meta_path', 'modules', 'path', 'path_hooks', 'path_importer_cache', 'platform', 'prefix', 'ps1', 'ps2', 'pycache_prefix', 'set_asyncgen_hooks', 'set_coroutine_origin_tracking_depth', 'setdlopenflags', 'setprofile', 'setrecursionlimit', 'setswitchinterval', 'settrace', 'stderr', 'stdin', 'stdout', 'thread_info', 'unraisablehook', 'version', 'version_info', 'warnoptions'] Without arguments, >>> a = [1, 2, 3, 4, 5] >>> import fibo >>> fib = fibo.fib >>> dir() ['__builtins__', '__name__', 'a', 'fib', 'fibo', 'sys'] Note that it lists all types of names: variables, modules, functions, etc.
>>> import builtins >>> dir(builtins) ['ArithmeticError', 'AssertionError', 'AttributeError', 'BaseException', 'BlockingIOError', 'BrokenPipeError', 'BufferError', 'BytesWarning', 'ChildProcessError', 'ConnectionAbortedError', 'ConnectionError', 'ConnectionRefusedError', 'ConnectionResetError', 'DeprecationWarning', 'EOFError', 'Ellipsis', 'EnvironmentError', 'Exception', 'False', 'FileExistsError', 'FileNotFoundError', 'FloatingPointError', 'FutureWarning', 'GeneratorExit', 'IOError', 'ImportError', 'ImportWarning', 'IndentationError', 'IndexError', 'InterruptedError', 'IsADirectoryError', 'KeyError', 'KeyboardInterrupt', 'LookupError', 'MemoryError', 'NameError', 'None', 'NotADirectoryError', 'NotImplemented', 'NotImplementedError', 'OSError', 'OverflowError', 'PendingDeprecationWarning', 'PermissionError', 'ProcessLookupError', 'ReferenceError', 'ResourceWarning', 'RuntimeError', 'RuntimeWarning', 'StopIteration', 'SyntaxError', 'SyntaxWarning', 'SystemError', 'SystemExit', 'TabError', 'TimeoutError', 'True', 'TypeError', 'UnboundLocalError', 'UnicodeDecodeError', 'UnicodeEncodeError', 'UnicodeError', 'UnicodeTranslateError', 'UnicodeWarning', 'UserWarning', 'ValueError', 'Warning', 'ZeroDivisionError', '_', '__build_class__', '__debug__', '__doc__', '__import__', '__name__', '__package__', 'abs', 'all', 'any', 'ascii', 'bin', 'bool', 'bytearray', 'bytes', 'callable', 'chr', 'classmethod', 'compile', 'complex', 'copyright', 'credits', 'delattr', 'dict', 'dir', 'divmod', 'enumerate', 'eval', 'exec', 'exit', 'filter', 'float', 'format', 'frozenset', 'getattr', 'globals', 'hasattr', 'hash', 'help', 'hex', 'id', 'input', 'int', 'isinstance', 'issubclass', 'iter', 'len', 'license', 'list', 'locals', 'map', 'max', 'memoryview', 'min', 'next', 'object', 'oct', 'open', 'ord', 'pow', 'print', 'property', 'quit', 'range', 'repr', 'reversed', 'round', 'set', 'setattr', 'slice', 'sorted', 'staticmethod', 'str', 'sum', 'super', 'tuple', 'type', 'vars', 'zip'] 6.4. Packages¶Packages are a way of structuring Python’s module namespace by using “dotted module names”. For example, the module name Suppose you want to design a collection of modules (a “package”) for the uniform handling of sound files and sound data. There are many different sound file formats (usually recognized by their extension, for example: sound/ Top-level package __init__.py Initialize the sound package formats/ Subpackage for file format conversions __init__.py wavread.py wavwrite.py aiffread.py aiffwrite.py auread.py auwrite.py ... effects/ Subpackage for sound effects __init__.py echo.py surround.py reverse.py ... filters/ Subpackage for filters __init__.py equalizer.py vocoder.py karaoke.py ... When importing the package, Python searches through the directories on The Users of the package can import individual modules from the package, for example: import sound.effects.echo This loads the submodule sound.effects.echo.echofilter(input, output, delay=0.7, atten=4) An alternative way of importing the submodule is: from sound.effects import echo This also loads the submodule echo.echofilter(input, output, delay=0.7, atten=4) Yet another variation is to import the desired function or variable directly: from sound.effects.echo import echofilter Again, this loads the
submodule echofilter(input, output, delay=0.7, atten=4) Note that when using Contrarily, when using syntax like 6.4.1. Importing * From a Package¶Now what happens when the user writes The only solution is for the package author to provide an explicit index of the package. The __all__ = ["echo", "surround", "reverse"] This would mean that If import sound.effects.echo import sound.effects.surround from sound.effects import * In this example, the
Although certain modules are designed to export only names that follow certain patterns when you use Remember, there is nothing wrong with using 6.4.2. Intra-package References¶When packages are structured into subpackages (as with the You can also write relative imports, with the from . import echo from .. import formats from ..filters import equalizer Note that relative imports are based on the name of the current module. Since
the name of the main module is always 6.4.3. Packages in Multiple Directories¶Packages support one more special attribute,
While this feature is not often needed, it can be used to extend the set of modules found in a package. Footnotes 1In fact function definitions are also ‘statements’ that are ‘executed’; the execution of a module-level function definition adds the function name to the module’s global namespace. How do you import a package in Python?Importing module from a package
We can import modules from packages using the dot (.) operator. Now, if this module contains a function named select_difficulty() , we must use the full name to reference it. Now we can directly call this function.
What does it mean to import a package in Python?What is Importing? Importing refers to allowing a Python file or a Python module to access the script from another Python file or module. You can only use functions and properties your program can access. For instance, if you want to use mathematical functionalities, you must import the math package first.
What is __ import __ in Python?__import__() . This means all semantics of the function are derived from importlib. __import__() . The most important difference between these two functions is that import_module() returns the specified package or module (e.g. pkg. mod ), while __import__() returns the top-level package or module (e.g. pkg ).
What is a package in Python example?A package is basically a directory with Python files and a file with the name __init__ . py. This means that every directory inside of the Python path, which contains a file named __init__ . py, will be treated as a package by Python.
|