Python User Input & String Formatting Mastery: Beginner's Guide

Python User Input

Python allows for user input. This means that we can ask for the user's input. The method in Python 3.6 is slightly different from that of Python 2.7. Python 3.6 supports the input() methods. Python 2.7 supports the raw_input() methods.

When you enter the username into the following example, the username is printed on the screen:

Python 3.6

username = input("Enter username:")
print("Username is: " + username)

Python 2.7

username = raw_input("Enter username:")
print("Username is: " + username)

Python will stop executing the input() functions when the user enters some input:

How to Handle User Input in Python

Python has quickly become an indispensable skill for developers working in fields such as Data Science. But working with user input can be tricky: errors arise and there may be limitations inherent to the language that must be taken into account.

Python by default treats input as strings. If the input does not conform to an integer range, a ValueError exception could occur.

Handling user inputs effectively

How a program handles user input is an integral component of its functionality, particularly for programs reliant on it (such as calculators). Effective user input management is essential to prevent errors and provide clear feedback to the user; Python programming language offers various tools for this task such as its built-in input() function as well as more sophisticated modules like argparse.

The input() function enables coders to receive information from users through keyboard input. It can be used for entering values or characters and combined with other functions for more complex commands. It also contains split() which separates input into multiple values by means of delimiters such as commas.

By default, the input() function returns user input as a string; however, you can use type conversion functions to convert this string to another data type - for instance if asking users about their age using int() as part of this form submission process, int() would convert their response into an integer value.

The input() function differs significantly from its predecessor, raw_input(), which was the standard means of processing user input up until Python 3. Raw_input evaluates any code entered by users, which could present security risks; real-world programs should avoid using this function and parse their input using full Python syntax instead.

Handling input errors

As you are developing a Python program, it is critical that errors from user inputs are handled appropriately. This includes validation, length limitations, input/output separation and security features. Furthermore, exception handling should also be implemented to handle run time errors; this can prevent your program from terminating prematurely or crashing and make debugging simpler.

Python's input() function enables you to read user input from a keyboard. It awaits until Enter key is pressed before reading text from standard input stream and returning data as string; alternatively you may use functions like int() and float() for more complex conversion.

When using the input() function, it's essential to be mindful that it's a runtime function and may not allow for accurate evaluation of whether any value entered by users is valid or invalid. For instance, if they enter "23," for example, then input() won't recognize it as an integer and throw an error; to prevent this from occurring, you can add a try-except block into your code to protect itself from this scenario.

A try-except block prevents the execution of any invalid statements within it, and is highly recommended when dealing with production code or programs that accept user input. In particular, using user modules or plugins which evaluate Python code at runtime instead of built-in functions such as input() will give more reliable results than simply depending on built-in functions like input() for runtime evaluation of code. This feature should especially benefit production environments or those taking user input.

Separating user input from program output

User input is an integral component of any program, from keyboard input to mouse clicks or track-pad movement. Python offers powerful tools that help collect user data and display it on screen.

Python's input() function accepts text from users and converts it into strings for display on screen until pressed enter, at which time program resumes normal flow with input returned back into it.

Python's input() function can be useful, but it has some restrictions that make it less so. For instance, it returns user input as strings rather than different data types - making input validation important in order to ensure programs receive valid and readable data.

There are various methods available in Python for validating user input, including using sanitizing functions and length limiting. Another powerful Python feature that can help is list comprehension; this feature combines multiple inputs onto one line for easy verification of data inputs - this method may help reduce errors and security risks by merging multiple fields together into one string.

Providing clear feedback to the user

User input is an essential aspect of programming, enabling developers to interact with users and collect valuable information. This data may then be used for tasks or output generation. It's vital that information from users remains valid and readable; there are various techniques for doing this depending on what kind of input it is being submitted and its necessity within a program.

Python provides many tools for managing user input efficiently. One such function is input(), which takes in lines from users and converts it to strings. If you need integer or other types of inputs instead, other functions must be used instead.

Python provides two similar but more flexible input functions:

 raw_input() and input(). raw_input() accepts any type of input and returns it as string, making it especially helpful for advanced applications. Furthermore, raw_input() supports Python code evaluators; these should only ever be used for testing purposes or small examples and should never be trusted with production code or untrustworthy user input.

Python String Formatting 

You can use the Format() Method to format a string so that it displays as you expect.

String Format()

The Format() Method allows you to format specific parts of a text.

You may not be able to control certain parts of the text. Perhaps they are from a user-input or a database?

To control these values, you can add placeholders in the text (curly brackets ), and then run the values through format():

Example

Add a placeholder to the page where you wish to display the price.

The parameter inside the curly braces will specify the conversion method:

price = 49
txt = "The price is {} dollars"
print(txt.format(price))

Format the price displayed as a two-decimal number:

txt = "The price is {:.2f} dollars"

Multiple Values

Add more values by adding them to the format() method.

print(txt.format(price, itemno, count))

Add more placeholders to the list:

quantity = 3
itemno = 567
price = 49
myorder = "I want {} pieces of item number {} for {:.2f} dollars."
print(myorder.format(quantity, itemno, price))

Index Numbers

Use index numbers (a number within the curly brackets 0) to ensure that the values are in the right placeholders.

Example

quantity = 3
itemno = 567
price = 49
myorder = "I want {0} pieces of item number {1} for {2:.2f} dollars."
print(myorder.format(quantity, itemno, price))

If you wish to refer to a value multiple times, then use the index number.

age = 36
name = "John"
txt = "His name is {1}. {1} is {0} years old."
print(txt.format(age, name))

Named Indexes

If you want to use named indexes, you can enter a name in the curly brackets carname. However, you will need names for the parameter values txt.format()(carname = "Ford").

myorder = "I have a {carname}, it is a {model}."
print(myorder.format(carname = "Ford", model = "Mustang"))