with statement replaces former
try...finally blocks in Python. It ensures that clean-up code is executed. For example, it closes open files before leaving the block. Consider this code example (assuming this code is stored in a file named
with open('code.py') as code: print(code.read())
The output of this code would be the code itself (for nerds: a piece of code that generates itself is called a Quine):
''' OUTPUT with open('code.py') as code: print(code.read()) '''
No matter what goes wrong inside the
with block, Python will close the open file before moving on in the code. This way, you don’t need to enclose the code with a
Single Expression ‘With’ Statement in One Line
Problem: Can you write the
with statement in a single line of code?
Solution: Yes, you can write the
with statement in a single line of code if the loop body consists only of one statement:
with open('code.py') as code: print(code.read())
Exercise: The following interactive code throws an error if you run it. Fix the bug and run the correct code!
Multi Expression ‘With’ Statement in One Line
If the body consists of multiple statements, you can use a semicolon between the different statements:
with open('code.py') as code: print('The code:') print(code.read())
The previous code block becomes:
with open('code.py') as code: print('The code:'); print(code.read())
Note that in this particular instance, the semantics actually change because the code reads its own source file! But in all other cases, the semantics remain the same.
As soon as you have nested blocks like a
for loop inside a
with block, you cannot use this approach anymore because the code would become ambiguous. Believe it or not but the indentation serves a real purpose in Python! 😉
Nested Indentation Blocks in a One-Line ‘With’ Statement
If you know the Finxter tutorials, you also know that I seldomly conclude with such a statement “XYZ is impossible” because in most cases, it isn’t. If you’re in doubt whether you can compress an algorithm into a single line of code—don’t. You can compress all algorithms into a single line!
Consider the following example with a
for loop inside a
with open('code.py') as code: for i in range(10): print(code.read())
Problem: One-Linerize a nested with block!
Wrong Solution: Write it into a single line:
Correct Solution: Replace the inner for loop with a list comprehension statement!
with open('code.py') as code: [print(code.read()) for i in range(10)]
While this code runs and solves the problem, please note that the chosen example does not make a lot of sense. The file is read only once—even if you place it into a for loop. The reason is that the file reader is done reading the file after the first iteration. In subsequent iterations it only reads the remaining characters (there aren’t any) so the output is not 10x only 1x the file contents.
Where to Go From Here?
Enough theory. Let’s get some practice!
Coders get paid six figures and more because they can solve problems more effectively using machine intelligence and automation.
To become more successful in coding, solve more real problems for real people. That’s how you polish the skills you really need in practice. After all, what’s the use of learning theory that nobody ever needs?
You build high-value coding skills by working on practical coding projects!
Do you want to stop learning with toy projects and focus on practical code projects that earn you money and solve real problems for people?
🚀 If your answer is YES!, consider becoming a Python freelance developer! It’s the best way of approaching the task of improving your Python skills—even if you are a complete beginner.
If you just want to learn about the freelancing opportunity, feel free to watch my free webinar “How to Build Your High-Income Skill Python” and learn how I grew my coding business online and how you can, too—from the comfort of your own home.
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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.
While working as a researcher in distributed systems, Dr. Christian Mayer found his love for teaching computer science students.
To help students reach higher levels of Python success, he founded the programming education website Finxter.com that has taught exponential skills to millions of coders worldwide. He’s the author of the best-selling programming books Python One-Liners (NoStarch 2020), The Art of Clean Code (NoStarch 2022), and The Book of Dash (NoStarch 2022). Chris also coauthored the Coffee Break Python series of self-published books. He’s a computer science enthusiast, freelancer, and owner of one of the top 10 largest Python blogs worldwide.
His passions are writing, reading, and coding. But his greatest passion is to serve aspiring coders through Finxter and help them to boost their skills. You can join his free email academy here.