Python stdin to string

How do you read from stdin in Python?

One of the simplest methods to read from stdin is using the Python built-in input() function, which prompts the user to enter input from the keyboard and returns a string containing the input.

Standard input, or stdin for short, is a fundamental concept in computer programming. It allows programs to read input from the user or from other programs. In this article, we will explain how to read input from stdin in Python using the input() function and three other popular methods.

1. Quick Examples of Reading from Stdin in Python

These examples will give you a high-level idea of how to read input from the standard input stream in Python using four different methods. We will discuss these methods in detail.

2. Python input() Method to Read from stdin

This is the most common method to take input from stdin (standard input) in Python. The input() is a built-in function that allows you to read input from the user via stdin. When you call input() , python waits for the user to enter a line of text, and then returns the line as a string.

The input() function always returns a string. So if you need to process the input as a different type (such as an integer or a floating-point number). You will need to use a type conversion function like int() or float().

If you don’t provide a prompt string as an argument to input(), Python will still wait for the user to enter input, but there will be no visible prompt on the console.

3. Use sys.stdin to take Input from Stdin

The stdin is a variable in the sys module in Python that can be used to read from the console or stdin. It is a file-like object that represents the input stream of the interpreter. To use sys.stdin to read input from stdin, you can simply call the readline() method on it to read one line at a time

This code will read input from stdin one line at a time and print each line to the console with whitespace stripped off the ends.

You can also use sys.stdin.read() to read all input at once as a string. See the example below:

sys.stdin is a file-like object, which means you can use all the methods and attributes of file objects on it. It includes like readline(), read(), close(), etc.

Unlike input() , sys.stdin does not automatically convert the input to a string, so you may need to call str() or bytes() to convert the input to the desired type.

4. fileinput.input() – Input form Stdin

We have the fileinput module in Python, which is another alternative to read input from either stdin or one or more files specified as command-line arguments.

5. open(0).read() – Read from Stdin

If you prefer a more concise way to read input from stdin in Python, you can use the open() function to create a file object that represents stdin, and then use the read() method to read all the input at once as a string.

The open(0) creates a file object that represents stdin (file descriptor 0), and calling read() on that object reads all the input at once.

This can be a convenient way to read input if you know it’s small enough to fit in memory. But it can be slower and less memory-efficient than using other methods like iterating over stdin line by line.

open(0) may not be available on all systems or platforms. So be sure to test your code thoroughly if you plan to use this method.

6. Summary and Conclusion

We have explained how to read from stdin in Python, Stdin is short for Standard Input. You have learned how to use input() function and other methods along that to read from stdin. I hope this article was helpful. Let me know if you have any questions.

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How to Read from stdin in Python

While we believe that this content benefits our community, we have not yet thoroughly reviewed it. If you have any suggestions for improvements, please let us know by clicking the “report an issue“ button at the bottom of the tutorial.

1. Using sys.stdin to read from standard input

Python sys module stdin is used by the interpreter for standard input. Internally, it calls the input() function. The input string is appended with a newline character (\n) in the end. So, you can use the rstrip() function to remove it. Here is a simple program to read user messages from the standard input and process it. The program will terminate when the user enters “Exit” message.

import sys for line in sys.stdin: if 'Exit' == line.rstrip(): break print(f'Processing Message from sys.stdin **********') print("Done") 

Hi Processing Message from sys.stdin *****Hi ***** Hello Processing Message from sys.stdin *****Hello ***** Exit Done 

Notice the use of rstrip() to remove the trailing newline character so that we can check if the user has entered “Exit” message or not.

2. Using input() function to read stdin data

We can also use Python input() function to read the standard input data. We can also prompt a message to the user. Here is a simple example to read and process the standard input message in the infinite loop, unless the user enters the Exit message.

while True: data = input("Please enter the message:\n") if 'Exit' == data: break print(f'Processing Message from input() **********') print("Done") 

The input() function doesn’t append newline character to the user message.

3. Reading Standard Input using fileinput module

We can also use fileinput.input() function to read from the standard input. The fileinput module provides utility functions to loop over standard input or a list of files. When we don’t provide any argument to the input() function, it reads arguments from the standard input. This function works in the same way as sys.stdin and adds a newline character to the end of the user-entered data.

import fileinput for fileinput_line in fileinput.input(): if 'Exit' == fileinput_line.rstrip(): break print(f'Processing Message from fileinput.input() **********') print("Done") 

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How to Read From stdin in Python

Reading from stdin (standard input) in Python is a common programming task that helps create interactive I/O programs. Stdin reads keyboard inputs from a user, files, or data streams.

Python offers several different methods to read from stdin depending on the type of problem.

This guide provides three methods to show how to read standard input from stdin in Python.

Method 1: Read From stdin Using sys.stdin

The sys module contains a stdin method for reading from standard input. Use this method to fetch user input from the command line.

Import the sys library and use the stdin method in a for loop. See the example below for a demonstration:

import sys print('Write a message and press Enter: ') for line in sys.stdin: line = line.rstrip() print(f'Message from stdin: ') break

The code does the following:

• Reads user input from the keyboard ( sys.stdin ).
• Removes new lines from the user entry ( rstrtip() ).
• Prints back the entered message by appending an f-string.
• Exits the for loop ( break ).

The program expects user input, prints the entered text stream, and returns to the command line.

Method 2: Read From stdin Using the input() function

The second way to read input from stdin in Python is with the built-in input() function. Enter a descriptive message as a value, and save the output into a variable.

message = input('Enter a message:') print(f'Your name is: ')

The program saves the input from stdin into a variable ( name ) and returns the value.

Method 3: Read from stdin by Using fileinput.input()

The fileinput Python library contains the input() function, which allows reading file names from standard input.

The method allows passing file names as a function or command-line arguments. In both cases, the file’s contents are read as input from stdin. Below is a demonstration of both use cases.

Files as Function Arguments

To pass file names as the fileinput.input() arguments, the files must be located in the same directory as the script.

For example, if the current directory contains two files (file1.txt and file2.txt), use the following code to print the file contents line by line:

import fileinput with fileinput.input(files=('file1.txt', 'file2.txt')) as f: for line in f: print(line)

The with statement helps open a file stream, uses the file names as the function’s input, then goes through each line in the file using a for loop. As a result, the contents of the files print to the console.

Files as Command Line Arguments

An alternative way to read files is to provide the file names as command-line arguments. Use this method when reading different files each time.

The following code shows how to read files provided as command-line arguments:

import fileinput for f in fileinput.input(): print(f)

Save the code and run with the following:

python3 test.py file1.txt file2.txt

The code goes through the list of files and prints the file contents to the console.

You now know three different methods to read input from stdin in Python. Standard input is an essential programming skill to get a user’s input into a program.

Next, learn about file handling in Python or see how to take user input and create a calculator with Python.

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