Python sys Module

sys is a module in the Python standard library that provides functions for interacting with the Python interpreter and its environment.

Through the sys library, you can access variables and functions related to the Python interpreter, such as command-line arguments, standard input/output, program exit, etc.

Importing the sys Library

Before using the sys library, you need to import it first. The import method is as follows:

import sys

Example

import sys
import os

# List all attributes and methods of the os module
print(dir(os))

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Common Features of the sys Library

1. Command-Line Arguments

sys.argv is a list containing command-line arguments. sys.argv[0] is the script name, and subsequent elements are the arguments passed to the script.

Example Code:

Example

import sys

print("Script name:", sys.argv[0])
print("Argument list:", sys.argv[1:])

How to Run:

python script.py arg1 arg2

Output Result:

Script name: script.py
Argument list: ['arg1', 'arg2']

2. Program Exit

sys.exit() is used to exit the program. You can pass an integer as the exit status code. Typically, 0 indicates success, and non-zero values indicate errors.

Example Code:

Example

import sys

print("Program starts")
sys.exit(0)
print("This line will not execute")

3. Standard Input/Output

sys.stdin, sys.stdout, and sys.stderr represent standard input, standard output, and standard error streams respectively. You can redirect these streams to implement custom input/output behavior.

Example Code:

Example

import sys

# Redirect standard output to a file
with open('output.txt', 'w') as f:
    sys.stdout = f
    print("This content will be written to output.txt")

# Restore standard output
sys.stdout = sys.__stdout__
print("This content will be displayed on the console")

4. Python Version Information

sys.version and sys.version_info provide the current Python interpreter’s version information.

Example Code:

Example

import sys

print("Python version:", sys.version)
print("Version info:", sys.version_info)

Output Result:

<code>Python version: 3.9.7 (default, Aug 31 2021, 13:28:12) 
[GCC 7.5.0]
Version info: sys.version_info(major=3, minor=9, micro=7, releaselevel=&#39;final&#39;, serial=0)
</code>

5. Module Search Path

sys.path is a list containing the paths that the Python interpreter searches when importing modules. You can modify this list to add custom module search paths.

Example Code:

Example

import sys

print("Module search path:", sys.path)
sys.path.append('/custom/path')
print("Updated module search path:", sys.path)

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sys Module Common Attributes

Attribute	Description
sys.argv	Command-line argument list, sys.argv[0] is the script name
sys.path	Python module search path (PYTHONPATH)
sys.modules	Dictionary of loaded modules
sys.platform	Operating system platform identifier (e.g., 'win32', 'linux', 'darwin')
sys.version	Python interpreter version information
sys.executable	Absolute path of the Python interpreter
sys.stdin	Standard input stream (file object)
sys.stdout	Standard output stream (file object)
sys.stderr	Standard error stream (file object)
sys.byteorder	Byte order ('little' or 'big')
sys.maxsize	Maximum integer value (2**31-1 or 2**63-1)

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sys Module Common Methods

Method	Description
sys.exit([status])	Exit the program. status=0 indicates normal exit
sys.getsizeof(obj)	Return the memory bytes occupied by the object
sys.getdefaultencoding()	Get the default string encoding (usually 'utf-8')
sys.setrecursionlimit(limit)	Set the recursion depth limit (default 1000)
sys.getrecursionlimit()	Get the current recursion depth limit
sys.getrefcount(obj)	Return the reference count of the object
sys.exc_info()	Get the current exception information ((type, value, traceback))
sys.settrace(tracefunc)	Set the debug tracing function
sys.setprofile(profilefunc)	Set the profiling function