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 'n' and pass the result into the exec(...) function. You can run this script from the outside (command line, shell, terminal) by using the command 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 loop with a nested if statement in the for loop body. You want to run this in a single line from your command line?

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 x. If x takes an even value, it prints the loop variable i.

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

Table of Contents

Method 1: exec()

You can write any source code into a string and run the string using the built-in exec() function in Python. This is little known—yet, hackers often 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 'n' in your string:

# Method 1
exec('x = 10nfor 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:

'''
0
9
2
7
4
'''

Try it yourself in our interactive code shell:

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

This is how it looks in my Win 10 powershell:

PS C:Usersxcent> python -c "exec('x = 10nfor 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:

# 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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By the end of the book, you’ll know how to write Python at its most refined, and create concise, beautiful pieces of “Python art” in merely a single line.

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