Readline from stdin python

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.

 import fileinput import sys # Using input() function input_line = input("Enter text: ") # Using sys.stdin print("Enter text (type 'q' to quit): ") for line in sys.stdin: line = line.rstrip() if line == "q": break # Using fileinput.input() print("Enter text (type 'q' to quit): ") for line in fileinput.input(): line = line.rstrip() if line == "q": break # Using open(0).read() print("Enter text (type 'q' to quit): ") text = open(0).read().rstrip() lines = text.split("\n") for line in lines: if line == "q": break 

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.

 # Prompt on terminal asking for input name = input("Enter your name: ") print(f"Hello, !") 

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().

 age = input("Enter your age: ") # The type of age will be string print(type(age)) # We need to convert it to other types age = int(age) print(f"age: !") 

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

 # Read input in Loop import sys for line in sys.stdin: print(line.strip()) 

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:

 # Read all at once import sys data = sys.stdin.read() print(f"You entered characters") 

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.

 import sys # Read a single line of input from stdin input_line = sys.stdin.readline() # Convert the input to an integer try: input_int = int(input_line) except ValueError: print("Error: Input must be an integer") sys.exit(1) # Perform some operation with the input integer result = input_int * 2 # Output the result print(result) 

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.

 # Use loop and fileinput import fileinput for line in fileinput.input(): print(line.strip()) 

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.

 input_str = open(0).read() print(input_str) 

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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Best Ways to Read Input in Python From Stdin

When you are writing a python code, the most basic and essential thing is data. Data on which you can perform mathematical and arithmetic operations to finally get the results you desire. However, to perform these operations, you need to input the data into your code. Although there are various ways you can input data in your code, we are going to specifically cover information about python read input from stdin.

What Is Stdin?

Stdin is standard input. Standard input is basically a stream that creates a file in which it stores inputs from which the program can access the input data and write output accordingly. Additionally, there are many ways you can read input from stdin in python programming. We will cover those methods in this article.

Read Input From Stdin Using Input()

In the first method, we will see how we can read standard input using the ‘input()’ function. Taking input using the ‘input()’ function is quite simple. Let’s directly understand the syntax and usage of the function with the help of an example:

x = input("write your input: ") #define a variable to store input in print(x) #print the variable to get output in form of input string, variable or float.

write your input: Hello world Hello world

In the above example, we use a variable in which we store the input and print that variable to print the stored input. We can also perform mathematical and arithmetic operations on this variable if the input form is an integer or any other computable form.

Read Input From Stdin Using Sys Module

The sys module offers many functions, one of which is ‘sys.stdin()’. Again let’s understand better with the help of an example:

import sys for line in sys.stdin: if 'Exit' == line.rstrip(): break print(f'The input entered : ') print("Program Exited")

Hello The input entered : Hello Welcome to python pool The input entered : Welcome to python pool Exit Program Exited

In this example we use ‘sys.stdin’ function which internally calls ‘input()’ function. Moreover, ‘sys.stdin’ takes new line input after every sentence. In addition to that, we have used the ‘rstrip()’ function, which checks if the user has entered Exit as an input string or not. If the user enters Exit as an input, it stops the program. Furthermore, ‘sys.stdin’ is case sensitive, so the string you set as your exit string should match the input string case-wise too.

Read Input From Stdin Using Fileinput Module

Fileinput module can read and write multiple files from stdin. It takes files as an argument and returns text present in it. Besides that, you can also read and write other formats of files. Again let’s understand the usage and syntax of this module.

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

testdataa.txt This a sample text file

This example shows a simple implementation of fileinput module in which we use the ‘fileinput.input()’ function to read stdin input. Further, if you want to know how to read a file line by line, check out this post.

Read Binary Input Data From Stdin

Sometimes you may require to read a file containing binary data. You can use three modules side by side to read stdin of binary form. The following three modules are os, sys, and msvcrt. To understand how to read binary data from stdin, let’s see an example.

import os, sys, msvcrt msvcrt.setmode (sys.stdin.fileno(), os.O_BINARY) input = sys.stdin.read('testdata1.bin') print len (input)

We use three modules to read binary files from the standard input sys module is used for taking stdin, the os module is used for reading files in binary format, and finally, the msvcrt module is used to set the line-end translation mode for the file descriptor.

Sys.readline Reading From Stdin

The ‘sys.readline()’ is a function offered by the sys module. It can read lines from the stdin stream. In addition to that, this function can read the escape character. Moreover, we can also set the parameter to read characters, meaning we can set the function to read a specific amount of characters from the input. Let us see an example to see how we can use this function.

import sys inputone = sys.stdin.readline() print(inputone) inputtwo = sys.stdin.readline(4) print(inputtwo)

Hello Hello\n Welcome Welc

As you can see in input one, there is a space after “Hello “ the readline function identifies that escape character and prints it. Further in input-two, the parameter to read characters is set to four. Therefore, it only reads four characters from the input.

Read Input From Stdin Line By Line

You can also read input from stdin line by line. To achieve this, you can use the sys module and ‘sys.stdin.readlines()’ function.

import sys data = sys.stdin.readlines()

The above code shows how you can use the ‘sys.stdin.readlines()’ function and how its syntax is defined.

Read Stdin Until Specific Character

Sometimes you might want to read standard input until a specific character, like any specific integer or a string, to do that. You can use the sys module and create a loop that terminates when we enter a specific character. Let’s take an example to understand this.

import sys def read_until_character(): x = [ ] minus = False while True: character = sys.stdin.read(1) if not character: break if character == '2' and minus: x.pop() break else: minus = (character == '-') x.append(char) return ''.join(buf) print(read_until_character())

11 21 34 -23 22 -11 2 11 21 34

As you can see in this example, our code reads input until we enter the -2 character and prints the output up to the previous character of -2.

FAQs on Python Read Input from Stdin

Stdin is standard input. Read from standard input means sending data to a stream that is used by the program. It is a file descriptor in Python.

You can use fileinput module and use fileinput.input function to read one or more text files at the same time.

To read from stdin, you can use one of three methods: sys.stdin, ‘input()’ function, or fileinput module.

You can use ‘sys.readline()’ function to read the escape characters, and further, you can also define the parameter to read characters.

Conclusion

Finally, we can conclude that there are many ways you can read input from standard input (stdin). You can use any of the methods as per your requirements for the program. Moreover, you can use these methods and develop your own logic because you can use the functions we have discussed creatively and efficiently to achieve your desired results.

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