Ten first Python exercises for practice

How to use this list

Work through them in order without looking at ready solutions. Stuck for half an hour? Look at a hint, then close it and write your own.

After each one, check the edge cases: empty input, a single element, all elements identical. That's what people most often forget at interviews.

The ten

1. Word frequency in a text. Read a file, count how often each word appears, print the ten most common.

Trains: files, strings, dictionaries, sorting.

2. Renaming files. Walk a folder and rename every file to a pattern: add a date, remove spaces, lowercase everything.

Trains: the file system, strings. Useful in real life too.

3. Parsing a table. Read a comma-separated file, compute the sum and mean of one column, print the rows above the mean.

Trains: structured data, type conversion, filtering.

4. Balanced brackets. Given a string with brackets of several kinds, decide whether they're correctly nested.

Trains: using a list as a stack. A classic interview problem.

5. Two numbers with a given sum. Find two numbers in a list that sum to a target. First by brute force, then in one pass with a dictionary.

Trains: understanding why a dictionary beats a list here.

6. Weather from a public source. Request data from a public service, parse the response, print it readably.

Trains: network requests, parsing, handling connection errors.

7. Expense tracking in a file. A program that takes commands: add an expense, show the monthly total, show totals by category. Data survives restarts.

Trains: persisting state, program structure, dates.

8. Checking sites for availability. Given a list of addresses, check each and print which don't respond.

Trains: networking, exception handling, lists.

9. Password generator. With parameters: length, digits, symbols. With validation of the parameters.

Trains: randomness, command-line arguments, input checking.

10. Log parsing. A file of log lines: find all errors, group them by type, print a summary for a period.

Trains: everything together. A good final check.

What to do afterwards

If all ten went without great pain, move to your own project. Beyond this point, exercises teach less than building something real.

A good exit test: take problem seven and take it to the point where you'd use it daily. That isn't an exercise any more — it's a first project.