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python -c and scripts

Learn to run scripts from the command line.

What is a script file?

You can save Python code to a file and run it from the terminal. This file is called a script and has the .py extension.

For example you write print("Hello") into hello.py and run it with python3 hello.py.

Unlike the REPL, a script file runs all the code from top to bottom. The REPL runs line by line. For large programs you use a script file.

python3 -c for a one-liner

Sometimes you want to run a short piece of code without saving it to a file. For this you use the python3 -c flag:

python3 -c 'print("Hello")'

-c is short for 'command'. It runs the code inside the quotes and exits. It is very handy for a quick calculation or check.

Unlike a script file this is not permanent; the code is not saved.

Practice Complete the script

Complete the script below so that it prints Script ran to the screen with print. Add an explanatory comment at the top.

Starter code

main.py
# This script prints a message to the screen

Sample solution

main.py
# This script prints a message to the screen
print("Script ran")

Expected output

Script ran

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 Write the script extension

Question 
# file name: hello____
print("Hello")
Answer 
# file name: hello.py
print("Hello")

Explanation: Python scripts are saved with the .py extension.

2 Which command runs merhaba.py?

  • python3 merhaba.py Correct answer
  • execute merhaba.py
  • run merhaba.py
  • merhaba.py run

Explanation: python3 merhaba.py runs the file.

3 Match each way to run Python

Term Meaning
python3 file.py Run a script
python3 -c '...' Run a one-liner
python3 Start the REPL
exit() Leave the REPL

All lessons in Beginner

1 Python basics

  1. What is Python?
  2. REPL and print
  3. Comments
  4. Indentation blocks
  5. python -c and scripts
  6. Summary - Python basics

2 Variables

  1. Variable assignment
  2. Multiple assignment
  3. Naming variables
  4. id and type
  5. Swapping variables
  6. Summary - Variables

3 Data types

  1. int and float
  2. bool
  3. str basics
  4. None
  5. Type conversion
  6. Summary - Data types

4 Project: Calculator

  1. Project design
  2. Add/subtract
  3. Multiply/divide
  4. Error handling
  5. Putting it together

5 Operators

  1. Arithmetic
  2. Comparison
  3. Logical
  4. Bitwise
  5. Membership and identity
  6. Summary - Operators

6 String basics

  1. f-string
  2. Concatenation
  3. str.format
  4. Raw strings
  5. Triple-quote
  6. Summary - String basics

7 Conditionals

  1. The if statement
  2. elif and else
  3. Nested if
  4. Truthiness
  5. Conditional expression
  6. Summary - Conditionals

8 Loops

  1. The for loop
  2. range
  3. The while loop
  4. break and continue
  5. Loop else
  6. Summary - Loops

9 Project: Shopping cart

  1. Cart design
  2. Adding items
  3. Calculating totals
  4. Updating quantity
  5. Putting it together

10 Lists

  1. Declaring lists
  2. Index and slice
  3. List methods
  4. in and count
  5. Sorting lists
  6. Summary - Lists

11 List comprehension

  1. Comprehension basics
  2. Filtered comprehension
  3. Dict and set comprehension
  4. Nested comprehension
  5. Generator expression
  6. Summary - List comprehension

12 Tuple, set and dict

  1. Tuple
  2. Set
  3. Dict basics
  4. Dict methods
  5. Dict comprehension
  6. Summary - Tuple, set and dict

13 Functions

  1. def
  2. return
  3. Docstring
  4. Default parameters
  5. *args and **kwargs
  6. Summary - Functions

14 Function parameters

  1. Positional parameters
  2. Keyword parameters
  3. Keyword-only
  4. Positional-only
  5. Type hints basics
  6. Summary - Function parameters

15 Project: To-do CLI

  1. Task model
  2. Adding tasks
  3. Listing tasks
  4. Completing tasks
  5. Putting it together

16 Advanced string methods

  1. split and join
  2. strip, lstrip, rstrip
  3. replace
  4. find and index
  5. startswith, endswith
  6. Summary - Advanced strings

17 Input and output

  1. input()
  2. int/float conversion
  3. print parameters
  4. f-string formatting
  5. sys.argv
  6. Summary - Input and output

18 Error handling

  1. try/except
  2. else and finally
  3. raise
  4. Exception hierarchy
  5. Custom exceptions
  6. Summary - Error handling

19 Modules

  1. import
  2. from import
  3. as alias
  4. __name__ == '__main__'
  5. Standard library
  6. Summary - Modules

20 Beginner final

  1. Project design
  2. Data model
  3. Business logic
  4. Error handling
  5. Putting it together