Read or update environment variables
A script needs configuration supplied by its execution environment.
Python · Module
os
Python’s os module provides portable interfaces to operating-system functionality, including environment variables, process parameters, files, directories, and file descriptors. Use os.path for pathname manipulation and specialized modules for higher-level file operations.
How it works
The os module exposes portable interfaces to operating-system facilities. Use it for process environment access, current-directory operations, file-descriptor work, and other system interactions; use os.path for pathname manipulation and higher-level modules such as shutil or tempfile for specialized tasks.
Syntax
import os
os.system(command)
os.stat(path, *, dir_fd=None, follow_symlinks=True)Parameters
| Name | Type | Description |
|---|---|---|
command | str | Command string to execute in a subshell. |
path | path-like object or file descriptor | Path or file descriptor whose status is requested by os.stat(). |
dir_fd | int or None | Optional directory file descriptor for relative path resolution in functions that support it. |
follow_symlinks | bool | Whether symbolic links are followed by functions that provide this option. |
Returns
Return values depend on the selected os function; os.system() returns the command’s status, while os.stat() returns file-status information.
Key points
- os is the standard-library gateway to operating-system features while presenting common interfaces where possible.
- Python normally represents filenames, command-line arguments, and environment variables as strings.
- os.system(command) runs the supplied command string through a subshell.
- os.stat() obtains status information from either a path or a file descriptor.
- Use os.path for higher-level pathname operations instead of assembling path logic manually.
Common mistakes
- Text is the normal representation for names, arguments, and environment variables, but some operating-system interfaces also require bytes.
- Do not use os as the default abstraction for every filesystem task; choose open() for file I/O and os.path for pathname operations.
Example: Inspect the process environment
import os
print(os.getcwd())
os.environ["CARD_EXAMPLE"] = "ready"
print(os.environ["CARD_EXAMPLE"])
Shows the current working directory and reads a value from the process environment.
When to use it
Work with process directories
A backend task must inspect or change its working-directory context.
Inspect files and descriptors
A tool needs operating-system file metadata or lower-level descriptors.
Run a system command
A script must invoke a host command through the shell.
Interview questions
QWhat is the purpose of the os module?
The os module provides a portable interface to operating-system-dependent functionality. It covers areas such as environment variables, process parameters, files and directories, and file descriptors.
Follow-up: Which module should handle pathname manipulation? Use os.path; higher-level file and directory operations are handled by shutil.
QHow do you access environment variables with os?
The process environment is exposed through os.environ, which maps environment-variable names to values. The documentation describes both keys and values as strings.
Follow-up: Why might bytes matter? Some systems require names or values to be encoded or decoded before passing them to the operating system.
QWhat does os.system() do?
os.system(command) executes a command string in a subshell. It is therefore an interface to the host shell rather than a direct Python implementation of the command.
Follow-up: What should be considered before using it? Shell behavior and operating-system differences apply, so a more specialized subprocess interface may be preferable when precise process control is needed.
Related
os.pathopen()fileinputtempfileshutilos.environos.stat()os.system()