03 - Print and Input

Print()

The print() function in Python is used to output data to the console. It can accept multiple arguments and display them in various formats.

print(*objects, sep=' ', end='\n', file=sys.stdout, flush=False)

• objects: The values to be printed, separated by commas.
• sep: The separator between the objects. Default is a space ' '.
• end: The string appended at the end of the output. Default is a newline '\n'.
• file: The output is directed to this file object (default is sys.stdout).
• flush: If True, the output is flushed immediately (default is False).

Key Parameters

sep (Separator)

• sep is used to specify a separator between multiple values in the print function. By default, it is a space ' ', but you can change it to any string you want.

print("apple", "banana", "cherry", sep=", ")  # Output: apple, banana, cherry

end

• end is used to append a string after the printed output. By default, it is '\n' (a newline character), which means the next output will appear on a new line. You can modify this to print everything on the same line or add any custom string.

print("Hello", end=" ")
print("world!")  # Output: Hello world!

f-strings (Formatted Strings)

• f-strings (formatted string literals) allow embedding expressions inside string literals using curly braces {}. Introduced in Python 3.6, f-strings provide an easy and efficient way to embed variable values into strings.

name = "Alice"
age = 30
print(f"My name is {name} and I am {age} years old.")
# Output: My name is Alice and I am 30 years old.

You can also apply formatting options to the variables inside f-strings:

pi = 3.14159265358979
print(f"Pi to 2 decimal places: {pi:.2f}")  # Output: Pi to 2 decimal places: 3.14

Input()

The input() function is used to take input from the user via the console. It always returns a string, so if you need a different data type, you’ll need to explicitly cast the value.

user_input = input("Prompt message: ")

• Prompt message: A message that is displayed to the user before waiting for input.

Getting Multiple Inputs

You can get multiple inputs from the user using split() to split the input string into a list based on a delimiter.

# Getting multiple inputs
name, age = input("Enter your name and age: ").split()
print(f"Name: {name}, Age: {age}")

In this case, the user would input a string like Alice 25, and the values would be split into the name and age variables.

Type Casting

Since input() always returns a string, you might need to cast the input to another data type (like int, float, etc.).

age = int(input("Enter your age: "))  # Convert the string to an integer
print(f"Next year, you'll be {age + 1} years old.")

Similarly, for floating-point numbers:

height = float(input("Enter your height in meters: "))  # Convert to float

Using eval()

The eval() function can evaluate a string as a Python expression. It allows you to execute more complex expressions or mathematical formulas input by the user. Be cautious when using eval() since it can execute arbitrary code, which may be unsafe if you’re not in control of the input.

result = eval(input("Enter a mathematical expression: "))
print(f"The result is: {result}")

If the user enters 5 + 3, the output would be The result is: 8.

Command-Line Arguments

Python allows you to pass command-line arguments to your script, which can be accessed using the sys.argv list. This is useful for passing configuration or input data to your program when running it from the command line.

Using sys.argv

1. Importing sys: To use sys.argv, you need to import the sys module.

2. sys.argv: This is a list containing all the command-line arguments passed to the Python script, where sys.argv[0] is the script name itself.

import sys

# Print all arguments passed to the script
print(f"Arguments passed to the script: {sys.argv}")

# Access individual arguments
if len(sys.argv) > 1:
    print(f"First argument: {sys.argv[1]}")

Command-Line Argument Example:

Run the Python script from the terminal:

python script.py arg1 arg2 arg3

Output:

Arguments passed to the script: ['script.py', 'arg1', 'arg2', 'arg3']
First argument: arg1

len(sys.argv)

len(sys.argv) returns the number of arguments passed to the script, including the script name. This can be used to check if enough arguments are provided.

import sys

if len(sys.argv) < 2:
    print("Usage: python script.py <arg1> <arg2> ...")
else:
    print(f"Received arguments: {sys.argv[1:]}")