Python sys Module: Essential System Interface

import sys
 
# sys.argv is the argument list
# sys.argv[0] is the script name
print(f"Script: {sys.argv[0]}")
print(f"Arguments: {sys.argv[1:]}")
 
# Example: python script.py arg1 arg2
# sys.argv = ['script.py', 'arg1', 'arg2']

import sys
 
# Standard streams
sys.stdout.write("This goes to stdout\n")
sys.stderr.write("This goes to stderr\n")
 
# Read from stdin
line = sys.stdin.readline()
 
# Redirect output
original_stdout = sys.stdout
sys.stdout = open('output.txt', 'w')
print("This goes to file")
sys.stdout = original_stdout

import sys
 
# Exit with status code
sys.exit(0)    # Success
sys.exit(1)    # Error
sys.exit("Error message")  # Prints to stderr, exits with 1
 
# Check if running interactively
if hasattr(sys, 'ps1'):
    print("Interactive mode")

import sys
 
# Version string
print(sys.version)
# '3.11.0 (main, Oct 24 2022, 00:00:00) [GCC 11.2.0]'
 
# Version tuple
print(sys.version_info)
# sys.version_info(major=3, minor=11, micro=0, ...)
 
# Check version
if sys.version_info >= (3, 10):
    print("Python 3.10+")
 
# Implementation
print(sys.implementation.name)  # 'cpython'

import sys
 
# Platform identifier
print(sys.platform)  # 'linux', 'darwin', 'win32'
 
# Byte order
print(sys.byteorder)  # 'little' or 'big'
 
# Max values
print(sys.maxsize)    # Maximum list/string size
print(sys.maxunicode) # Maximum Unicode code point
 
# Executable path
print(sys.executable)  # '/usr/bin/python3'

import sys
 
# Where Python looks for modules
print(sys.path)
 
# Add to path at runtime
sys.path.insert(0, '/my/custom/path')
 
# Or append
sys.path.append('/another/path')
 
# Remove from path
sys.path.remove('/unwanted/path')

import sys
import json
 
# All loaded modules
print(list(sys.modules.keys())[:10])
 
# Check if module is loaded
if 'json' in sys.modules:
    print("json is loaded")
 
# Get module object
json_module = sys.modules['json']
 
# Reload a module (remove from cache)
if 'mymodule' in sys.modules:
    del sys.modules['mymodule']

import sys
 
# Size of object in bytes
print(sys.getsizeof([1, 2, 3]))      # ~88 bytes
print(sys.getsizeof("hello"))        # ~54 bytes
print(sys.getsizeof({"a": 1}))       # ~64 bytes
 
# Reference count
x = [1, 2, 3]
print(sys.getrefcount(x))  # Usually 2+ (includes temporary)
 
# Recursion limit
print(sys.getrecursionlimit())  # Default: 1000
sys.setrecursionlimit(2000)     # Increase if needed

import sys
 
try:
    1 / 0
except:
    # Get exception info
    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
 
def trace_calls(frame, event, arg):
    if event == 'call':
        print(f"Calling: {frame.f_code.co_name}")
    return trace_calls
 
# Enable tracing
sys.settrace(trace_calls)
 
# Your code here
def example():
    pass
 
example()
 
# Disable tracing
sys.settrace(None)
 
# Profiling hook
sys.setprofile(profile_callback)

import sys
 
# Display hook (modifies REPL output)
def custom_display(value):
    if value is not None:
        print(f"Result: {value!r}")
 
sys.displayhook = custom_display
 
# Exception hook (unhandled exceptions)
def custom_excepthook(exc_type, exc_value, exc_tb):
    print(f"Unhandled exception: {exc_value}")
 
sys.excepthook = custom_excepthook

import sys
 
# Command line flags
print(sys.flags)
# sys.flags(debug=0, inspect=0, interactive=0, optimize=0, ...)
 
# Check if optimized
if sys.flags.optimize:
    print("Running with -O")
 
# Float info
print(sys.float_info.max)  # Maximum float value
print(sys.float_info.epsilon)  # Smallest difference
 
# Int info
print(sys.int_info.bits_per_digit)  # Bits in digit

import sys
 
# Intern a string for faster comparison
a = sys.intern("hello")
b = sys.intern("hello")
 
print(a is b)  # True (same object)
 
# Useful for repeated string comparisons
keys = [sys.intern(k) for k in ["key1", "key2", "key3"]]

import sys
 
def get_caller_name():
    """Get name of calling function."""
    frame = sys._getframe(1)
    return frame.f_code.co_name
 
def example():
    print(f"Called by: {get_caller_name()}")
 
def main():
    example()
 
main()  # "Called by: main"

import sys
 
# Default encoding
print(sys.getdefaultencoding())  # 'utf-8'
 
# stdin/stdout encoding
print(sys.stdin.encoding)   # 'utf-8'
print(sys.stdout.encoding)  # 'utf-8'
 
# File system encoding
print(sys.getfilesystemencoding())  # 'utf-8'

import sys
 
# Script guard
if __name__ == '__main__':
    if len(sys.argv) < 2:
        print(f"Usage: {sys.argv[0]} <arg>", file=sys.stderr)
        sys.exit(1)
    main(sys.argv[1])
 
# Platform-specific code
if sys.platform == 'win32':
    path_sep = '\\'
else:
    path_sep = '/'
 
# Python version check
if sys.version_info < (3, 8):
    print("Python 3.8+ required")
    sys.exit(1)