Python sys Module Guide

import sys
 
# Script name and arguments
print(sys.argv[0])  # Script name
print(sys.argv[1:]) # Arguments
 
# Example: python script.py arg1 arg2
# sys.argv = ["script.py", "arg1", "arg2"]

import sys
 
# Exit with status code
sys.exit(0)  # Success
sys.exit(1)  # Error
 
# Exit with message (goes to stderr)
sys.exit("Error: something went wrong")
 
# Same as
print("Error: something went wrong", file=sys.stderr)
sys.exit(1)

import sys
 
# Standard streams
sys.stdin   # Input stream
sys.stdout  # Output stream
sys.stderr  # Error stream
 
# Read from stdin
line = sys.stdin.readline()
all_input = sys.stdin.read()
 
# Write to stdout
sys.stdout.write("Hello\n")
 
# Write to stderr
sys.stderr.write("Error!\n")
print("Error!", file=sys.stderr)
 
# Flush output
sys.stdout.flush()

import sys
from io import StringIO
 
# Capture output
old_stdout = sys.stdout
sys.stdout = StringIO()
 
print("This is captured")
 
output = sys.stdout.getvalue()
sys.stdout = old_stdout
 
# Or use contextlib
from contextlib import redirect_stdout
 
with redirect_stdout(StringIO()) as f:
    print("Captured")
output = f.getvalue()

import sys
 
# List of paths Python searches for imports
print(sys.path)
 
# Add path at runtime
sys.path.insert(0, "/path/to/modules")
 
# Or append
sys.path.append("/another/path")

import sys
 
# Dictionary of loaded modules
sys.modules
 
# Check if module is loaded
if "json" in sys.modules:
    print("json is loaded")
 
# Get module object
json_module = sys.modules.get("json")
 
# Reload module (use importlib instead)
import importlib
importlib.reload(module)

import sys
 
# Version string
sys.version  # "3.11.0 (default, ...)"
 
# Version tuple
sys.version_info
# sys.version_info(major=3, minor=11, micro=0, ...)
 
# Check version
if sys.version_info >= (3, 10):
    print("Python 3.10+")
 
if sys.version_info < (3, 9):
    sys.exit("Python 3.9+ required")

import sys
 
sys.platform    # "darwin", "linux", "win32"
sys.executable  # Path to Python interpreter
sys.prefix      # Installation prefix
 
# Platform-specific code
if sys.platform == "darwin":
    print("macOS")
elif sys.platform == "linux":
    print("Linux")
elif sys.platform == "win32":
    print("Windows")

import sys
 
# Size of object in bytes
sys.getsizeof([1, 2, 3])
 
# Recursion limit
sys.getrecursionlimit()  # Default: 1000
sys.setrecursionlimit(2000)
 
# Reference count
sys.getrefcount(object)

import sys
 
# Default encoding
sys.getdefaultencoding()  # Usually "utf-8"
 
# Filesystem encoding
sys.getfilesystemencoding()
 
# Stdin/stdout encoding
sys.stdin.encoding
sys.stdout.encoding

import sys
 
try:
    raise ValueError("test")
except:
    exc_type, exc_value, exc_tb = sys.exc_info()
    print(f"Type: {exc_type}")
    print(f"Value: {exc_value}")
    print(f"Traceback: {exc_tb}")

import sys
 
MIN_VERSION = (3, 9)
 
if sys.version_info < MIN_VERSION:
    sys.exit(f"Python {MIN_VERSION[0]}.{MIN_VERSION[1]}+ required")

import sys
 
if not sys.stdin.isatty():
    # Input is piped
    data = sys.stdin.read()
else:
    # Interactive mode
    data = input("Enter data: ")

import sys
 
for i in range(100):
    sys.stdout.write(f"\rProgress: {i+1}%")
    sys.stdout.flush()
print()  # Newline at end

import sys
from pathlib import Path
 
# Add parent directory
sys.path.insert(0, str(Path(__file__).parent.parent))
 
# Now can import from project root
from mypackage import module

import sys
 
def debug_info():
    print(f"Python: {sys.version}")
    print(f"Platform: {sys.platform}")
    print(f"Executable: {sys.executable}")
    print(f"Encoding: {sys.getdefaultencoding()}")

import sys
 
# Arguments
sys.argv[0]           # Script name
sys.argv[1:]          # Arguments
 
# Exit
sys.exit(0)           # Exit with code
sys.exit("Error")     # Exit with message
 
# I/O
sys.stdin.read()
sys.stdout.write(s)
sys.stderr.write(s)
 
# Paths
sys.path              # Module search paths
sys.executable        # Python path
 
# Version
sys.version_info      # Version tuple
sys.platform          # OS platform
 
# Memory
sys.getsizeof(obj)    # Object size
sys.getrecursionlimit()