When importing modules in Python, top-level code runs automatically. This can set up initial states but may cause unintended side effects. Understanding this behavior is crucial for managing module execution and avoiding unexpected consequences.
To prevent unintended execution, use the
###if___name___==_'[__main__](https://www.fiveableKeyTerm:__main__)':_0###
conditional block. This separates code for
import from direct execution, allowing modules to be both importable and executable. The
[__name__](https://www.fiveableKeyTerm:__name__)
variable plays a key role in controlling module behavior.
Module Behavior and Top-Level Code
Code execution during import
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Python executes all top-level code (statements outside functions or classes) when a module is imported
Allows module to set up initial state (initialize variables, define constants, establish connections)
Be aware of code running during import to understand module's behavior and side effects
Module might modify global state or perform resource-intensive tasks (file I/O, network requests)
Unintended consequences if not carefully managed (performance impact, unexpected behavior)
Top-level code execution contributes to the module's global scope and module namespace
Prevention of unintended execution
Role of name variable
__name__
is a built-in Python variable holding the name of current module
Set to '__main__'
when module run directly
Set to module name when imported
Checking __name__
value controls module behavior based on usage context
Different code paths for standalone program vs. library usage
Common use cases:
Executing code only when run directly (running tests, command-line interface)
Preventing code execution during import (user interaction, resource-intensive tasks)
Conditionally importing dependencies or configuring module based on usage context
Leverages __name__
to create modules that are both importable and executable
Flexibility in how module can be used (library or standalone program)
Enables modular and reusable code design