How to Run a Python Script

Run a Python script in 4 steps

1. Save your code in a file that ends in .py, for example hello.py.
2. Open a terminal: Command Prompt or PowerShell on Windows, Terminal on macOS and Linux.
3. Go to the folder that holds the file, for example cd Documents/python.
4. Type python hello.py (py hello.py on Windows, python3 hello.py on macOS and Linux) and press Enter. The output appears in the terminal.

The command on Windows, macOS and Linux

On Windows, py is the Python launcher that the installer from python.org adds. It finds the newest Python on the computer, so it works even when python is not on the PATH. On macOS and many Linux systems, python either does not exist or starts an old Python 2, which is why python3 is the safe choice there.

If the file is in another folder, give its path instead of changing folders: python3 ~/projects/hello.py on macOS and Linux, or py C:\Users\you\projects\hello.py on Windows. Put the path in quotes if it contains spaces.

Run a Python script online, without installing Python

On a school computer, a Chromebook, a tablet or any machine where you cannot install software, run the script in the browser. The editor runs real Python 3 with NumPy, pandas, Matplotlib and other common packages already installed, and asks for keyboard input when the script calls input().

import platform
import sys

print("Hello from Python", platform.python_version())
print("Script arguments:", sys.argv[1:])

name = input("What is your name? ")
print(f"Nice to meet you, {name}!")

numbers = [4, 8, 15, 16, 23, 42]
print("Sum:", sum(numbers), "Average:", sum(numbers) / len(numbers))

Run a Python script with arguments

Words after the file name are passed to the script in the list sys.argv. The first item is the script's own name, so the arguments start at sys.argv[1]. Each argument is a string; convert it with int() or float() when you need a number.

python3 greet.py Ada 3

import sys

# python greet.py Ada 3  ->  sys.argv == ["greet.py", "Ada", "3"]
name = sys.argv[1] if len(sys.argv) > 1 else "world"
times = int(sys.argv[2]) if len(sys.argv) > 2 else 1

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

For scripts with many options, the standard argparse module adds named options such as --count 3 and a --help message.

What if __name__ == "__main__": does

Python runs a file from top to bottom. Code inside if __name__ == "__main__": runs only when you start the file itself, not when another file imports it. Putting the script's work in a main() function and calling it there keeps the file usable both as a script and as a module.

def main():
    total = sum(range(1, 101))
    print("1 + 2 + ... + 100 =", total)


# This block runs when you start the file directly (python app.py),
# but not when another file imports it.
if __name__ == "__main__":
    main()

Run a Python script in VS Code, IDLE or PyCharm

• VS CodeInstall the Python extension, open the file and select the Run button (the triangle) in the top right, or press Ctrl+F5. The output appears in the terminal panel.
• IDLEComes with Python on Windows and macOS. Open the file with File, Open, then press F5 or choose Run, Run Module.
• PyCharmRight-click in the editor and choose Run, or press Shift+F10 after the first run.
• BrowserThe online Python editor runs the file with Run, steps through it with Debug, and shows variables in the Python visualizer.

Other ways to run Python code

Common errors when running a Python script

Next steps

Short lessons with code you can run, starting from the first program.

• Python Hello World: Your First Program
• Python input(): Read User Input with Examples
• Python Modules and Imports with Examples
• Python File Handling: Read and Write Files
• Python Try Except: Exception Handling with Examples
• Python Functions with Examples

Frequently asked questions