Python sys Module

sys is a powerful module that lets us access and alter various parts of the Python runtime environment. We can access several variables, constants, functions, and methods of the python interpreter. It is a built-in language and comes ready to use in the Python Standard Library. sys is a sub-module of the OS module.

Importing the sys Module in Python

We need to import the sys module using an import statement to use the functions that are available in the module. We can use the ‘import’ keyword to import the entire module or ‘from’ the keyword to import a specific function from the module. In our example, we use the import keyword.

Example of importing the sys module in Python

import sys
print(dir(sys))

Output

In the above code example, we imported the sys module. We can also notice that we used the Python built-in function dir() to print all objects in the sys module. We can see that there are a number of objects in the sys module for us to play with. Let’s see what some of those objects do in Python.

Objects in sys Module

argv

The variable contains a list of command-line arguments and either name or path of the script we are running. The name or path of the script is always at index 0 and the arguments always start from index 1.

Example on using argv in Python

script
import sys
print(sys.argv)

Terminal

(apple) (base) MacBook-Pro:Geeks apple$ python main.py Python Geeks

Output

base_exec_prefix

It has the same value as base_prefix. Unlike base_prefix, it is much more efficient.

Example on using base_exec_prefix in Python

import sys
print(sys.base_exec_prefix)

Output

base_prefix

It has the same value as prefix if we are not running a virtual environment. Unlike prefix, its value is set during Python startup.

Example on using base_prefix in Python

import sys
print(sys.base_prefix)

Output

byteorder

It indicates the native byte order. It has different values depending on the platform. On big-endian, its value is a string “big” and on small-endian, its value is a string “little”.

Example on using byteorder in Python

import sys
print(sys.byteorder)

Output

copyright

It is a string containing the copyright information of the Python version that we are currently using.

Example on using copyright in Python

import sys
print(sys.copyright)

Output

displayhook

It can be used to change the output behavior of an interactive python session. To do that, we have to assign a callable object which takes only a single argument to the displayhook.

Example on using displayhook in Python

import sys
def func(n): print("the number is", n)

sys.displayhook = func

x = 4
x

Output

executable

It is a string containing the executable binary’s absolute path for the Python interpreter. Python either returns None or an empty string if it can’t find the path.

Example on using executable in Python

import sys
print(sys.executable)

Output

exit([arg])

The function terminates the ongoing program. It can be used to exit the program and return to the command prompt or Python console. We can pass either a string or an integer to the function. Passing zero is considered to be a successful termination.

Example on using exit() in Python

import sys
print(sys.exit())

Output

getdefaultencoding()

The function returns a string containing the default string encoding.

Example on using getdefaultencoding() in Python

import sys
print(sys.getdefaultencoding())

Output

getrecursionlimit()

The function returns the current recursion limit of the Python interpreter.

Example on using getrecursionlimit() in Python

import sys
print(sys.getrecursionlimit())

Output

getrefcount(object)

The function returns a reference count of the passed object. Python automatically deletes the memory of a variable when its reference count becomes zero.

Example on using getrefcount() in Python

import sys
str = "PythonGeeks"
print(sys.getrefcount(str))

Output

getswitcinterval()

The function returns the thread switch interval of the Python interpreter in seconds.

Example on using getswitchinterval() in Python

import sys
print(sys.getswitchinterval())

Output

maxsize

The variable contains the highest Py_ssize_t value that can be stored. Its value depends on the CPU architecture.

Example on using maxsize in Python

import sys
print(sys.maxsize)

Output on 32-bit architecture

Output on 64-bit architecture

modules

This variable contains a dictionary of all modules which are currently imported and their corresponding paths.

Example on using modules in Python

import sys
import pandas
print(sys.modules['pandas'])

Output

path

Whenever we try to import a module, Python has to search for that module. The variable path contains a list of paths that Python uses to search for the specified module.

Example on using path in Python

import sys
print(sys.path)

Output

platform

It is a string containing the name of the platform on which we are executing our Python files.

Example on using platform in Python

import sys
print(sys.platform)

Output

prefix

It is a string containing the directory in which the platform-independent python files are installed.

Example on using prefix in Python

import sys
print(sys.prefix)

Output

setrecursionlimit(limit)

The function is used to set a maximum number of recursions Python executes. Setting a limit to recursions prevents our program from overflowing the stack and ultimately crashing the program. It raises a RecursionError if we exceed the limit.

Example on using setrecursionlimit() in Python

import sys

sys.setrecursionlimit(7)

def recur():
   return recur()
recur()

Output

setswitchinterval(interval)

The function sets the thread switch interval of the Python interpreter in seconds.

Example on using setswitchinterval() in Python

import sys

print(sys.getswitchinterval())
sys.setswitchinterval(1)
print(sys.getswitchinterval())

Output

settrace(frame, event, arg)

The function logs the tracebacks of the Python interpreter.

Example on using settrace() in Python

import sys

print("Code executed at line numbers")
def func(*args):
   print(str(args[0].f_lineno), end="\t")

def func1():
   return None

def func2():
   return func1()

sys.settrace(func)

func2()

Output

stdin

The built-in file object contains real values of the stdin at the start of a program and used at finalization. Using this with functions like readline() allows us to take input from the user.

Example on using stdin in Python

import sys
print("Your name is - ", sys.stdin.readline())

Input
sam

Output

stdout

stdout is a built-in file object that is used to display the output. We can use this to change the output behavior like redirecting output to a file rather than to a console.

Example on using stdout in Python

import sys
sys.stdout.write("Python Geeks")

Output

Example on using stdout to redirect the output to a file in Python

import sys

# saving the default output (console) for future use
default_output = sys.stdout
file = open('geeks.txt', 'w')
sys.stdout = file  # changing the output to file from console
print("PythonGeeks")
file.close()
# Changing the output to console from file
sys.stdout = default_output 
print("File Updated")

Output (Console)

stderr

stderr is a built-in file object which displays exceptions. We can redirect exceptions to a file instead of a console with the help of stderr.

Example on using stderr in Python

import sys
sys.stderr.write("Some Exception")

Output

Example on using stderr to redirect exceptions to a file in Python

import sys

# saving the default output (console) for future use
console = sys.stderr
file = open('geeks.txt', 'w')
sys.stderr = file  # changing the output to file from console
sys.stderr.write("Exception raised 1")  # Writing an exception
file.close()
# Changing the output to console from file
sys.stderr = console
sys.stderr.write("Exception raised 2")  # Writing an exception

Output (Console)

version

The variable returns a string containing the Python interpreter’s current version.

Example on using version in Python

import sys
print(sys.version)

Output

Python Interview Questions on the sys Module

Q1. The function in below has an infinite recursion. Add few lines to the existing code to prevent the function from calling itself more than 10 times.

Incomplete code

# Your code here

def add_num(num): return add_num(num+num)

add_num(1)

Ans 1. The completed code is as follows:

# Your code here
import sys
sys.setrecursionlimit(10)

def add_num(num): return add_num(num+num)

add_num(1)

Output

Q2. Write a program to input a word and print the first letter of that word without using the input() function.

Ans 2. Complete code is as follows:

import sys
word = sys.stdin.readline()
print(word[0])

Input
Hello

Output

Q3. Write a program to check the current version of Python. Print “Python2” if it less than 3 and print “Python3” if the version is 3 or greater than 3.

Ans 3. Complete code is as follows:

import sys

if int(sys.version[0]) < 3:
   print("Python2")
else:
   print("Python3")

Output

Q4. Write a program to print a variable without using the print() function.

Ans 4. Complete code is as follows:

import sys

var = "Good days"

sys.stdout.write(var)

Output

Q5. Write a program to input an integer and exit if the integer is 5, otherwise print the number.

Ans 5. Complete code is as follows:

import sys

num = int(input())

if num == 5:
   sys.exit()
else:
   print(num)

Input
5

Output

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1. Current
2. Review / Skip
3. Answered
4. Correct
5. Incorrect

1. Question 1 of 10

   1. Question

   sys is a ____ module.

   • Built-in
   • User-defined
   • Both A and B
   • None of the above
   Correct

   Incorrect
2. Question 2 of 10

   2. Question

   sys is a sub-module of the ____ module.

   • path
   • itertools
   • OS
   • platform
   Correct

   Incorrect
3. Question 3 of 10

   3. Question

    Which object can be used to take input from a user?

   • stdin
   • stdout
   • stderr
   • All of the above
   Correct

   Incorrect
4. Question 4 of 10

   4. Question

   Which object is used to get the Python interpreter’s current version?

   • version()
   • version
   • Version
   • version(args)
   Correct

   Incorrect
5. Question 5 of 10

   5. Question

   Which function is used to set a recursion limit?

   • recursionlimit()
   • setrecursion()
   • setlimit()
   • setrecursionlimit()
   Correct

   Incorrect
6. Question 6 of 10

   6. Question

   import sys

    

   print(sys.maxsize)

    

   • 9223372036854775807
   • 2147483647
   • Can not be determined
   • None of the above
   Correct

   Incorrect
7. Question 7 of 10

   7. Question

   import sys

    

   print(sys.stdout.write(“Python”))

    

   • ‘Python6’
   • Python
   • ‘Python’
   • Python6
   Correct

   Incorrect
8. Question 8 of 10

   8. Question

   Copyright (c) 2001-2020 Python Software Foundation.

   All Rights Reserved.

    

   Copyright (c) 2000 BeOpen.com.

   All Rights Reserved.

    

   Copyright (c) 1995-2001 Corporation for National Research Initiatives.

   All Rights Reserved.

    

   Copyright (c) 1991-1995 Stichting Mathematisch Centrum, Amsterdam.

   All Rights Reserved.

   • copyright()
   • copyright
   • getcopyrightinfo()
   • copyrightinfo()
   Correct

   Incorrect
9. Question 9 of 10

   9. Question

    

   import sys

    

   sys.setrecursionlimit(5)

   def natural_numbers(num):

    

      return natural_numbers(num+1)

    

   natural_numbers(1)

   • 1,2,3,4,5……..
   • 1,2,3,4,5
   • RecursionError
   • Program compiles but doesn’t print anything
   Correct

   Incorrect
10. Question 10 of 10

    10. Question

    import sys

     

    num = 24

    if 24 % 2 == 0:

       sys.exit()

       print(“Even Number”)

    else:

       print(“Odd Number”)

    • Even Number
    • Odd Number
    • AttributeError
    • Program compiles but doesn’t print anything
    Correct

    Incorrect

Conclusion

In this article, we learned about the sys module and ways of using the various functions and variables available in the module. Furthermore, please feel free to share them with us in the comment section if you have any queries.