What does sys.stdin read?

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I get how to open files, and then use Python's pre built in functions with them. But how does sys.stdin work?

for something in sys.stdin:
    some stuff here

lines = sys.stdin.readlines()

What's the difference between the above two different uses on sys.stdin? Where is it reading the information from? Is it via keyboard, or do we still have to provide a file?

So you have used Python's "pre built in functions", presumably like this:

file_object = open('filename')
for something in file_object:
    some stuff here

This reads the file by invoking an iterator on the file object which happens to return the next line from the file.

You could instead use:

file_object = open('filename')
lines = file_object.readlines()

which reads the lines from the current file position into a list.

Now, sys.stdin is just another file object, which happens to be opened by Python before your program starts. What you do with that file object is up to you, but it is not really any different to any other file object, its just that you don't need an open.

for something in sys.stdin:
    some stuff here

will iterate through standard input until end-of-file is reached. And so will this:

lines = sys.stdin.readlines()

Your first question is really about different ways of using a file object.

Second, where is it reading from? It is reading from file descriptor 0 (zero). On Windows it is file handle 0 (zero). File descriptor/handle 0 is connected to the console or tty by default, so in effect it is reading from the keyboard. However it can be redirected, often by a shell (like bash or cmd.exe) using syntax like this:

myprog.py < input_file.txt 

That alters file descriptor zero to read a file instead of the keyboard. On UNIX or Linux this uses the underlying call dup2(). Read your shell documentation for more information about redirection (or maybe man dup2 if you are brave).

What does sys.stdin read?, So you have used Python's "pre built in functions", presumably like this: file_object = open('filename') for something in file_object: some stuff  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 ( ) in the end. So, you can use the rstrip () function to remove it.

It is reading from the standard input - and it should be provided by the keyboard in the form of stream data.

It is not required to provide a file, however you can use redirection to use a file as standard input.

In Python, the readlines() method reads the entire stream, and then splits it up at the newline character and creates a list of each line.

lines = sys.stdin.readlines()

The above creates a list called lines, where each element will be a line (as determined by the end of line character).

You can read more about this at the input and output section of the Python tutorial.

If you want to prompt the user for input, use the input() method (in Python 2, use raw_input()):

user_input = input('Please enter something: ')
print('You entered: {}'.format(user_input))

Difference between input() and sys.stdin.readline(), readline() function. Input(), sys.stdin.readline(). The input takes input from the user but does not read escape character. Here are the examples of the python api sys.stdin.read taken from open source projects. By voting up you can indicate which examples are most useful and appropriate.

To get a grasp how sys.stdin works do following:

create a simple python script, let's name it "readStdin.py":

import sys
lines = sys.stdin.readlines()
print (lines)

Now open console any type in:

echo "line1 line2 line3" | python readStdin.py

The script outputs:

['"line1 line2 line3" \n']

So, the script has read the input into list (named 'lines'), including the new line character produced by 'echo'. That is.

How to Read from stdin in Python, There are three ways to read data from stdin in Python. sys.stdin input() built-in function fileinput.input() function 1. Using sys.stdin to read from. Sys.stdin.readline () Stdin stands for standard input which is a stream from which the program read its input data. This method is slightly different from the input () method as it also reads the escape character entered by the user. More this method also provides the parameter for the size i.e. how many characters it can read at a time.

for something in sys.stdin:
    some stuff here

The code above does not work as you expect because sys.stdin is a file handle - it is a file handle to the stdin. It will not reach the some stuff here line

lines = sys.stdin.readlines()

When the script above is run in an interactive shell, it will block the execution until a user presses Ctrl-D, which indicates the end of the input.

How to finish sys.stdin.readlines() input?, 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. Here is a simple program to read user messages from the standard input and process it. What the above means is that, sys.stdin is a File Object that is being used by Python interpreter for input. By default, sys.stdin is set to sys.__stdin__ which is input from the standard device. (The values of sys.stdin and sys.__stdin__ may however be None incase no console is connected)

According to me sys.stdin.read() method accepts a line as the input from the user until a special character like Enter Key and followed by Ctrl + D and then stores the input as the string.

Control + D works as the stop signal.

Example:

import sys

input = sys.stdin.read()
print(input)
tokens = input.split()
a = int(tokens[0])
b = int(tokens[1])
print(a + b)

After running the program enter two numbers delimited by space and after finishing press Control + D once or twice and you will be presented by the sum of the two inputs.

What's the difference between sys.stdin.read() and input , Hi Brendan, in this video the "sys.stdin.read()" is described as being able to take a newline and finish your entry with Control+D. input() would  Evan Demaris. 64,261 Points. on Nov 27, 2015. That sounds roughly correct, however input () also takes as an argument a string to use as a prompt, while sys.stdin.read () takes the length to read into the user-entered string as an optional argument instead (and provides no prompt - in the video, a print () was provided to serve as a prompt instead).

input() vs sys.stdin.read(), import sys s1 = input() s2 = sys.stdin.read(1) #type "s" for example s1 == "s" #​False s2 == In Python, how do I read a file line-by-line into a list? sys.stdin- A file-like object - call sys.stdin.read()to read everything. input(prompt)- pass it an optional prompt to output, it reads from stdin up to the first newline, which it strips. You'd have to do this repeatedly to get more lines, at the end of the input it raises EOFError. (Probably not great for golfing.)

sys.stdin.read Python Example, The following are code examples for showing how to use sys.stdin.read(). They are from open source Python projects. You can vote up the examples you like or​  #!/usr/bin/env python # catty.py import sys BUFFER_SIZE = 4096 while True: if sys. stdin. isatty (): # terminal present, read from stdin as text mode, buf = 'text', sys. stdin. readline (BUFFER_SIZE) else: # no tty, read from stdin as binary mode, buf = 'binary', sys. stdin. read (BUFFER_SIZE) if buf: sys. stderr. write ("read %s: %s" % (mode, buf)) elif buf == None: sys. stderr. write ("read %s: no data available " % mode) else: # empty array or empty string sys. stderr. write ("read %s

Python Tutorial 29, Your browser does not currently recognize any of the video formats available. Click here to visit Duration: 12:13 Posted: Jul 3, 2014 sys.excepthook (type, value, traceback) ¶ This function prints out a given traceback and exception to sys.stderr.. When an exception is raised and uncaught, the interpreter calls sys.excepthook with three arguments, the exception class, exception instance, and a traceback object.

Comments
  • Are you familiar with input()? Wherever input() would take input from, that's sys.stdin. That may be a terminal, or it may be directed from a file, or it might be coming from another program's output, or it might be something else, depending on how you invoked the program.
  • In python 3, a text stream.
  • So how is the standard input read differently when I use sys.stdin.readlines() instead of sys.stdin Does the second one reach each word? I'm still confused.
  • So how is the standard input read differently when I use sys.stdin.readlines() instead of sys.stdin Does the second one reach each word? I'm still confused.