4 useful Python command line switches

The Python 🐍 command has many different switches.

Here are the 4 switches I use the most:

1. -c cmd: program passed in as string;
2. -m mod: run library module as a script;
3. -i: inspect interactively after running script; and
4. -q: don't print version and copyright messages on interactive startup.

-c

The switch -c runs code directly from the command line. It doesn't open the REPL, and it is convenient for short, one-off expressions. The result isn't printed by default, so don't forget your print!

# What is the factorial of 15?
λ python -c "import math; print(math.factorial(15))"
1307674368000

# What is 2 + 2?
λ python -c "print(2 + 2)"
4

-m

The switch -m runs a module as a script. This will run an installed module's section that is inside if __name__ == "__main__":. The one I use the most is the module timeit to measure execution time:

λ python -m timeit -s "import math" "math.factorial(15)"
2000000 loops, best of 5: 167 nsec per loop

λ python -m timeit -s "import math" "math.factorial(150)"
200000 loops, best of 5: 1.52 usec per loop

-i

The switch -i stands for Inspect Interactively. By running your code with -i, after the script is done, you get a REPL session with the variables and functions from that script. Useful to play around with functions you just defined.

Suppose this is your file example.py:

x = 3
y = 5

def add(x, y):
    return x + y

If you run it with -i, you get to play around with the variables x and y and with the function add:

λ python -i example.py
>>> x
3
>>> y
5
>>> add(x, 10)
13

-q

The switch -q opens the REPL Quietly. What this means is that it opens the REPL without displaying all the version/platform information. I use it when recording videos and demoing things.

λ python -q
>>> # This is a standard REPL

Become a better Python 🐍 developer, drop by drop 💧

Get a daily drop of Python knowledge. A short, effective tip to start writing better Python code: more idiomatic, more effective, more efficient, with fewer bugs. Subscribe here.