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 takes an even value, it prints the loop variable
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
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 = 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:
''' 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
This is how it looks in my Win 10 powershell:
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:
# 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.