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input() and Output

PythonBy Updated

Reading a line from the user, why it is always text, and the print options worth knowing.

Overview

A note about this page

The editors here run Python in your browser, which has no keyboard attached to standard input, so input() raises OSError. The first program calls it inside a try so you can see exactly that, rather than the page pretending otherwise. Everything else uses a stand-in value, and behaves identically to what you would get from a real terminal.

input_basics.py

input_basics.py Python 3
Output

                    

                

                

            

            

                
print_options.py

                

                

                    
                    

                        print_options.py
                        Python 3
                    

                    

                        
                        

                            
                            
                        

                    

                    

                        
                        
                        
                    

                    

                        
Output

                        

                    

                

                

            

            

            

                

                    
Worth knowing

                    

                        
input() always returns a string, even when the user types digits.

                        
It needs a keyboard, so it raises in this in-browser runtime. On your machine it waits for a line.

                        
print(a, b, sep="-") changes the separator; end="" suppresses the newline.

                        
Convert with int() inside a try, because the user can type anything.

                    

                

            

        

    

    
    

        


            

                
input() and Output: A Practical Guide

                
input() reads one line from the user and returns it as a string — always a string, whatever it looks like. print() sends values the other way, with two options worth knowing.

            

            

                
                

                    
It is always text

                    
typed = input("Age: ")  # user types 42
typed + typed          # "4242", not 84
This is the first surprise everyone meets. input cannot know whether "42" is meant as a number, a house number or a password, so it does not guess. Convert explicitly:
age = int(input("Age: "))

                

                

                    
Convert defensively

                    
That one-liner raises ValueError the moment somebody types "forty" or presses enter on an empty line. For anything a real person will use:
def read_int(text, default=0):
    try:
        return int(text.strip())
    except (ValueError, AttributeError):
        return default
strip() first, because people type spaces.

                

                

                    
The prompt is an argument

                    
input("Your name: ") prints the prompt and reads on the same line. A separate print before it works too but puts the cursor on the next line, which reads worse.

                

                

                    
print has two useful options

                    
print("a", "b", sep="-")    # a-b
print(i, end=" ")         # no newline
sep sits between the values; the default is a single space. end goes after them; the default is a newline. end="" is how you build a line across several prints — and you then need a bare print() to close it, which the page demonstrates.

                

                

                    
print versus f-strings

                    
print calls str() on whatever you give it, which is fine for quick output. When the formatting matters — decimal places, alignment, thousands separators — build the string yourself with an f-string and print that. The two are complementary, not competing.
One detail worth noticing: printing a list shows its repr, so strings appear with quotes. ", ".join(items) is what you want when the output is for a person.

                

            


        

    


    



Check yourself
0 of 3
Answer without scrolling back up.
  1. The user types 42. What does `input()` return?
  2. What does `print(i, end=' ')` do?
  3. Why does `int(input())` need a try/except in real programs?





 Cheat sheet
input() and Output
input() reads one line from the user and returns it as a string — always a string, whatever it looks like. print() sends values the other way, with two options worth knowing.
PYTHON · vizlearn.in/python/input_and_output.html
More in Python
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About the author
Ashish Jangra builds and maintains VizLearn. Every module here is written and the visualisation behind it hand-built, so the numbers in a readout come from the same code that draws the picture. Corrections are genuinely welcome and get priority over everything else — if a page states something wrong, or an animation misrepresents what the algorithm does, get in touch.
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