Python Input and Output

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Python, as a high-level programming language, offers straightforward mechanisms for interacting with users: taking input and presenting output. This article will delve deeply into two fundamental aspects of this interaction: the print() function, which is used for output, and the input() function, which is used to collect input from users.

1. The print( ) Function

Basic Usage

At its core, the print() function sends specified messages to the console. The basic usage is straightforward. In Python, we can simply use the print() function to print output.

print("Hello, World!")


Hello, World!

Parameters and Their Use

While the basic usage is simple, the print() function comes with various parameters to enhance its functionality:

  1. *objects (var-positional): The values that you want to print. You can pass any number of them separated by commas.
  2. sep (str): The separator between the values. The default is a space (' ').
  3. end (str): The value that’s printed at the end. The default is a newline ('\n').
  4. file: The file-like object where the output is written. Default is sys.stdout (standard output).
  5. flush (bool): If set to True, the stream is forcibly flushed. Default is False.

Python print() with end Parameter

By default, every time you use the print() function in Python, a newline (\n) character is added to the end of the output. This behavior is because of the end parameter, which defaults to \n. But you can customize what gets added to the end of the print() output by specifying a different value for this parameter.

Basic Usage:

Here’s a simple example. Let’s print two strings on two consecutive lines, which is the default behavior:




Now, let’s modify the end parameter:

print("Hello", end=" ")


Hello World

By changing the end parameter to a space (" "), we’ve ensured that the two print statements output on the same line, with a space in between.

Practical Uses:

Printing on the same line: As shown above, this can be used to print multiple items on the same line.

Custom delimiters: You can use the end parameter to add custom delimiters or suffixes to your outputs:

print("Error:", end="!!")
print("File not found")


Error:!!File not found

No ending: Sometimes, you might not want any character or space at the end. Just use an empty string:

print("Loading", end="")



It might not seem different in the example above, but if you follow this print statement with another one, they’ll be on the same line without any space or character in between.

Creating patterns: If you’re trying to print patterns or tables, adjusting the end parameter can be handy.

for i in range(5):
    print("*", end="")



The end parameter of the print() function provides a way to customize the termination of the printed output. This might seem trivial, but it offers a great deal of flexibility, especially when you want to control the layout and presentation of your program’s output.

Python print() with sep parameter

When you provide multiple items to the print() function, by default, they are separated by a space. This behavior is because of the sep parameter, which defaults to a space (' '). However, you can modify this default behavior by specifying a different value for the sep parameter.

Basic Usage:

Here’s an illustration of the default behavior:

print("Hello", "World")


Hello World

The two strings are separated by a space because of the default value of sep.

Now, let’s modify the sep parameter:

print("Hello", "World", sep="-")



By specifying sep="-", we’ve instructed the print() function to use a hyphen as the separator between items.

Practical Uses:

Custom delimiters: This can be useful when you want to format data in a specific way, such as CSV:

print("Name", "Age", "Occupation", sep=",")



Formatting lists: When displaying lists, you might want to have custom formatting:

fruits = ["apple", "banana", "cherry"]
print(*fruits, sep=", ")


apple, banana, cherry

Note the use of *fruits. The asterisk (*) is the “splat” operator, which unpacks the elements of the list, so they’re passed to print() as separate arguments.

Multiline print: You can even use newline characters (\n) as separators:

print("This", "will", "be", "on", "different", "lines", sep="\n")



No separation: Sometimes, you might want no separation between items. Just use an empty string:

print("Hello", "World", sep="")



The sep parameter of the print() function allows you to define custom separators between multiple items passed to the function. It’s a simple yet effective tool for formatting output, especially when dealing with lists or structured data. By mastering the use of sep and other parameters of the print() function, you can have granular control over your program’s output in Python.

Formatting Outputs

The power of print() shines when combined with string formatting techniques, allowing for dynamic and styled outputs:

Using f-strings (Python 3.6+):

name = "Alice"
age = 30
print(f"{name} is {age} years old.")


Alice is 30 years old.

Using str.format():

print("{} is {} years old.".format(name, age))

Using % formatting:

print("%s is %d years old." % (name, age))

Redirection and Flushing

Python’s print() function can write to any file-like object. For instance, to write to a file:

with open("output.txt", "w") as f:
    print("Hello, World!", file=f)

This will write “Hello, World!” into the output.txt file.

The flush parameter is useful when you want to ensure that output is written immediately, which can be important in scenarios like real-time logging.

2. Taking User Input with the input( ) Function

Basic Usage

The input() function allows the program to pause and wait for the user to enter some information. The basic usage is:

user_input = input("Enter something: ")
print(f"You entered: {user_input}")

Here, “Enter something: ” is a prompt that will be displayed to the user. Whatever the user types in response will be stored in the user_input variable.

Casting and Type Conversion

By default, input() always returns a string. However, you often need to work with other data types. In such cases, you’ll need to convert (or “cast”) the input into the desired type:

num = int(input("Enter a number: "))
print(f"You entered the number {num}.")

Here, if the user enters “5”, the num variable will contain the integer 5.

Handling Exceptions

Since users can input anything, it’s crucial to handle possible exceptions during the casting process:

    num = int(input("Enter a number: "))
    print(f"You entered the number {num}.")
except ValueError:
    print("That's not a valid number!")


Interactivity is a fundamental aspect of many Python programs. Whether you’re crafting a command-line tool, a calculator, or just playing around in a REPL, understanding how to gather input and display output is crucial. The print() and input() functions offer simple yet powerful ways to facilitate this communication between the user and the machine. By mastering their usage and their various parameters and intricacies, you’re well on your way to making user-friendly Python programs.

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