132. Python's sys.argv

sys.argv is a list in Python, which contains the command-line arguments passed to a Python script. The first element, sys.argv[0], is the script name, and the subsequent elements (sys.argv[1:]) are the arguments provided by the user.

Here are some examples demonstrating how to use sys.argv to read command-line arguments in Python scripts:

1. Basic Example: Reading Command-Line Arguments

import sys

# Print the script name
print(f"Script name: {sys.argv[0]}")

# Print the command-line arguments passed to the script
print("Arguments passed:")
for arg in sys.argv[1:]:
    print(arg)

Example Usage:

python script.py arg1 arg2 arg3

Output:

Script name: script.py
Arguments passed:
arg1
arg2
arg3

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2. Accessing Specific Command-Line Arguments

import sys

# Check if the required number of arguments is passed
if len(sys.argv) < 3:
    print("Please provide at least two arguments.")
else:
    # Accessing specific arguments by index
    first_argument = sys.argv[1]
    second_argument = sys.argv[2]
    print(f"First argument: {first_argument}")
    print(f"Second argument: {second_argument}")

Example Usage:

python script.py hello world

Output:

First argument: hello
Second argument: world

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3. Using Command-Line Arguments for Calculations

import sys

# Ensure the correct number of arguments are provided
if len(sys.argv) != 3:
    print("Usage: python script.py <num1> <num2>")
    sys.exit(1)

# Convert arguments to integers
num1 = int(sys.argv[1])
num2 = int(sys.argv[2])

# Perform a simple calculation
sum_result = num1 + num2
print(f"The sum of {num1} and {num2} is: {sum_result}")

Example Usage:

python script.py 10 20

Output:

The sum of 10 and 20 is: 30

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4. Handling Optional Arguments

import sys

# Check if an optional argument is passed
if len(sys.argv) > 1:
    name = sys.argv[1]
    print(f"Hello, {name}!")
else:
    print("Hello, Guest!")

Example Usage:

python script.py Alice

Output:

Hello, Alice!

If no argument is provided:

python script.py

Output:

Hello, Guest!

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5. Argument Parsing with sys.argv for a Simple Command-Line Tool

import sys

def greet(name, times):
    for _ in range(times):
        print(f"Hello, {name}!")

# Ensure that the correct number of arguments is passed
if len(sys.argv) != 3:
    print("Usage: python script.py <name> <times>")
    sys.exit(1)

# Extract arguments and convert them to appropriate types
name = sys.argv[1]
times = int(sys.argv[2])

# Call the function
greet(name, times)

Example Usage:

python script.py Alice 3

Output:

Hello, Alice!
Hello, Alice!
Hello, Alice!

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6. Handling Invalid Arguments

import sys

# Ensure that the argument is a valid number
if len(sys.argv) != 2:
    print("Usage: python script.py <number>")
    sys.exit(1)

try:
    num = int(sys.argv[1])
    print(f"The square of {num} is {num ** 2}")
except ValueError:
    print("Please provide a valid integer.")

Example Usage:

python script.py 5

Output:

The square of 5 is 25

If an invalid argument is passed:

python script.py hello

Output:

Please provide a valid integer.

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Key Points:

• sys.argv provides access to the command-line arguments passed to a script.

• Indexing: sys.argv[0] is always the script name, and sys.argv[1:] contains the actual arguments.

• Error Handling: Ensure that the correct number of arguments is passed, and handle invalid inputs gracefully.