[Tut] How to Execute Multiple Lines in a Single Line Python From Command-Line?

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How to Execute Multiple Lines in a Single Line Python From Command-Line?

Summary: To make a Python one-liner out of any multi-line Python script, replace the new lines with a new line character

Code:

'\n'

and pass the result into the

Code:

exec(...)

function. You can run this script from the outside (command line, shell, terminal) by using the command

Code:

python -c "exec(...)"

.



Problem: Given a multi-line code script in Python. How to execute this multi-line script in a single line of Python code? How to do it from the command line?

Example: Say, you have the following for loopwith a nested if statement in the for loop body. You want to run this in a single line from your command line?

Code:

x = 10 for i in range(5): if x%2 == 0: print(i) else: print(x) x = x - 1 ''' 0 9 2 7 4 '''

The code prints five numbers to the shell. It only prints the odd values of

Code:

x

. If

Code:

x

takes an even value, it prints the loop variable

Code:

i

.

Let’s have a look at the three methods to solve this problem!

Method 1: exec()

You can write any source code into a string and run the string using the built-in

Code:

exec()

function in Python. This is little known—yet, hackersoften use this to pack malicious code into a single line that’s seemingly harmless.

If you have code that spans multiple lines, you can pack it into a single-line string by using the newline character

Code:

'\n'

in your string:

Code:

# Method 1 exec('x = 10\nfor i in range(5):\n if x%2 ==0: print(i)\n else: print(x)\n x = x-1')

This one-liner code snippet is semantically equivalent to the above nested for loop that requires seven lines of code! The output is the same:

Code:

''' 0 9 2 7 4 '''

Try it yourself in our interactive code shell:

https://repl.it/@finxter/YellowishGrowli...?lite=true

Exercise: Remove the else branch of this code. What’s the output? Run the code to check if you were right!

Method 2: From Command-Line | python -c + exec()

Of course, you can also run this code from your Win/Linux/Mac command line or shell.



Just make sure to use the

Code:

python -c

prefix and then pack the single-line multi-liner into a string value that is passed as an argument to the

Code:

python

program.

This is how it looks in my Win 10 powershell:

Code:

PS C:\Users\xcent> python -c "exec('x = 10\nfor i in range(5):\n if x%2 ==0: print(i)\n else: print(x)\n x = x-1')" 0 9 2 7 4

Method 3: Use Ternary Operator to One-Linerize the Code

Of course, you can also create your own semantically-equivalent one-liner using a bit of creativity and Python One-Liner skills (e.g., acquired through reading my book “Python One-Liners” from NoStarch)!

In this code, you use the ternary operator:

Code:

# Method 3 for i in range(5): print(10-i) if i%2 else print(i)

You can easily convince yourself that the code does the same thing in a single line!

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