Along with disrupting the functionality of the program, it also poses a major security risk. Your Email. Send OTP. Enter OTP. Choose a password At least 4 characters. Retype your password. Course Content Hide Player. I prefer choosing it because along with being free it also provides us with a number of features The professional edition is composed of a lot of extra features but community version will work fine for us at this level.
We are going to name our files file1. How does the import keyword work? There are two methods to use functions or variables after importing: The first one is to import using an object. For this, we usually import the whole module by using a simple import statement. When we use only the import keyword, we will import the resource directly, like this: import sklearn When we use the second syntax, we will import the resource from another package or module.
Active 5 years, 1 month ago. Viewed 28k times. I have two specific situations where I don't understand how importing works in Python: 1st specific situation: When I import the same module in two different Python scripts, the module isn't imported twice, right?
Improve this question. What happened when you ran the code? You may find these interesting: lucumr. They both treat imports in Python. Add a comment. Active Oldest Votes. Part 1 The module is only loaded once, so there is no performance loss by importing it again. It is also worth noting what exactly the import statement does: import foo binds the module name to the module object in the current scope, so if you modify foo.
Part 3 which doesn't even exist in your question :p The python documentation is extremely good and usually verbose - you find answer on almost every possible language-related question in there.
Improve this answer. ThiefMaster ThiefMaster k 77 77 gold badges silver badges bronze badges. To answer your first question: No, python does not get 'imported' twice. Casey Kuball Casey Kuball 6, 5 5 gold badges 39 39 silver badges 67 67 bronze badges. Looks like ThiefMaster beat me to answering the edit. Sign up or log in Sign up using Google. Sign up using Facebook. But what is a module exactly?
What gets assigned to the variable? In order to answer these questions, we need to give a bit more precise explanation: the statement import m searches for a module named m , creates a module object for that module, and assigns the module object to the variable. See how we differentiated between a module and a module object.
We can now define these terms. A module is anything that Python considers a module and knows how to create a module object for. This includes things like Python files, directories and built-in modules written in C. We'll look at the full list in the next section. The reason why we import any module is because we want to get an access to functions, classes, constants and other names that the module defines.
These names must be stored somewhere, and this is what module objects are for. A module object is a Python object that acts as a namespace for the module's names. The names are stored in the module object's dictionary available as m. Other fields are not really important for our discussion.
Python creates module objects implicitly for us. To see that there is nothing magical about this process, let's create a module object ourselves. We usually create Python objects by calling their types, like MyClass or set. Fortunately, such "unavailable" types can be found in the types standard module:.
How does the types module define ModuleType? It just imports the sys module any module will do and then calls type on the module object returned. We can do it as well:. No matter how we get ModuleType , once we get it, we can easily create a module object:. A newly created module object is not very interesting but has some special attributes preinitialized:. Most of these special attributes are mainly used by the import system itself, but some are used in the application code as well.
This observation may seem evident, but it's crucial. It comes from the fact that the dictionary of global variables is set to the dictionary of the current module:. The current module acts as a namespace for the execution of Python code. When Python imports a Python file, it creates a new module object and then executes the contents of the file using the dictionary of the module object as the dictionary of global variables. Thus, global variables are always attributes of some module, and this module is considered to be the current module from the perspective of the executing code.
Built-in modules are C modules compiled into the python executable. Since they are part of the executable, they are always available.
This is their key feature. The sys. Frozen modules are too a part of the python executable, but they are written in Python. Python code is compiled to a code object and then the marshalled code object is incorporated into the executable. Python freezes them because they implement the core of the import system and, thus, cannot be imported like other Python files. C extensions are a bit like built-in modules and a bit like Python files.
On the other hand, they are not a part of the executable but loaded dynamically during the import. Some standard modules including array , math and select are C extensions. Many others including asyncio , heapq and json are written in Python but call C extensions under the hood.
Technically, C extensions are shared libraries that expose a so called initialization function. They are usually named like modname. On my macOS, for example, any of these extensions will work:. And on Windows, you'll see. They are the result of compiling Python code to bytecode. More specifically, a. Its purpose is to reduce module's loading time by skipping the compilation stage.
When Python imports a. If the. However, we wouldn't call. Surprisingly, we can:. To learn more about. As we'll later see, we can customize the import system to support even more kinds of modules. So anything can be called a module as long as Python can create a module object for it given a module name. If module names were limited to simple identifiers like mymodule or utils , then they all must have been unique, and we would have to think very hard every time we give a new file a name.
For this reason, Python allows modules to have submodules and module names to contain dots. It adds the submodule to the module's dictionary and assigns the module to the variable a , so we can access the submodule as a module's attribute.
A module that can have submodules is called a package. This attribute tells Python where to look for submodules. When Python imports a top-level module, it searches for the module in the directories and ZIP archives listed in sys. Directories are the most common way to organize modules into packages. It can also be used to decouple the public API of a package from its internal implementation.
Suppose you develop a library with the following structure:. And you want to provide the users of your library with two functions: func1 defined in module1. It may be something you want, but you may also want to allow the users to import the functions like this:.
Python can import such packages perfectly fine:. Before version 3. PEP made these files unnecessary by introducing namespace packages in Python 3. Namespace packages solved another problem as well. They allowed developers to place contents of a package across multiple locations. For example, if you have the following directory structure:.
And both mylibs and morelibs are in sys. How does it work? When Python traverses path entries in the path sys. Namespace package do not shadow other modules because they have lower precedence during the module search. This statement imports a module named module and assign the specified attributes to the corresponding variables:. Note that the module variable is not available after the import as if it was deleted:.
When Python sees that a module doesn't have a specified attribute, it considers the attribute to be a submodule and tries to import it. So if module defines func and Class but not submodule , Python will try to import module.
If we don't want to specify explicitly the names to import from a module, we can use the wildcard form of import:.
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