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In this Python Tutorial chapter

0. Intro to Python Tutorial
1. History and Philosophy of Python
2. The Interpreter, an Interactive Shell
3. Execute a Script
4. Structuring with Indentation
5. Assignment Expressions
6. Data Types and Variables
7. Type Annotations
8. Operators
9. Sequential Data Types
10. List Manipulation
11. Shallow and Deep Copy
12. Dictionaries
13. Sets and Frozen Sets
14. Sets Examples
15. Keyboard Input
16. Conditional Statements
17. Structural Pattern Matching
18. Adventure Game with Structural Pattern Matching
19. While Loops
20. For Loops
21. Output with Print
22. Formatted Output
23. Working with Dictionaries and while Loops
24. Functions
25. Passing Arguments
26. Parameters And Arguments
27. Namespaces
28. Global vs. Local Variables and Namespaces
29. File Management
30. Modular Programming and Modules
31. Packages
32. Errors and Exception Handling

[input mini]

15. Keyboard Input

By Bernd Klein. Last modified: 29 Jun 2022.

The input Function

There are hardly any programs without any input. Input can come in various ways, for example, from a database, another computer, mouse clicks and movements or from the internet. Yet, in most cases the input stems from the keyboard. For this purpose, Python provides the function input(). input has an optional parameter, which is the prompt string.

If the input function is called, the program flow will be stopped until the user has given an input and has ended the input with the return key. The text of the optional parameter, i.e. the prompt, will be printed on the screen.

[Input via keyboard]

The input of the user will be returned as a string without any changes. If this raw input has to be transformed into another data type needed by the algorithm, we can use either a casting function or the eval function.

Let's have a look at the following example:

name = input("What's your name? ")
print("Nice to meet you " + name + "!")

What's your name? Melisa
Nice to meet you Melisa!

age = input("Your age? ")
print("So, you are already " + age + " years old, " + name + "!")

Your age? 26
So, you are already 26 years old, Melisa!

We save the program as "input_test.py" and run it:

 $ python input_test.py 
What's your name? "Frank"
Nice to meet you Frank!
Your age? 42
So, you are already 42 years old, Frank! 

We will further experiment with the input function in the following interactive Python session:

cities_canada = input("Largest cities in Canada: ")
print(cities_canada, type(cities_canada))

Largest cities in Canada: Toronto, Calgary, Montreal, Ottawa
Toronto, Calgary, Montreal, Ottawa <class 'str'>

cities_canada = eval(input("Largest cities in Canada: "))
print(cities_canada, type(cities_canada)) 

Largest cities in Canada: Toronto, Calgary, Montreal, Ottawa

population = input("Population of Toronto? ")
print(population, type(population))

Population of Toronto? 2615069
2615069 <class 'str'>

population = int(input("Population of Toronto? "))
print(population, type(population))

Population of Toronto? 2615069
2615069 <class 'int'>

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Differences between Python2 and Python3

The usage of input or better the implicit evaluation of the input has often lead to serious programming mistakes in the earlier Python versions, i.e. 2.x Therefore, in Python 3 the input function behaves like the raw_input function from Python2.

The changes between the versions are illustrated in the following diagram:

[Differences between input, raw_input and the Python versions]

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