Category Python List

When values from two iterables need to go into one Python list, the order of the loops determines the order of the results. A list comprehension builds a new list by evaluating an expression for the values its clauses supply.…

Saving Python list values for another program means putting them in a format it can read. JSON is a text format for values, and Python’s json module encodes a list as an array. This article shows how to write the…

Names and scores can be paired by position to make rows for a list of records. A Python list of tuples stores those rows in an outer list, with each tuple holding the ordered fields for one row. I’ll show…

To process a Python list one value at a time, your code needs a loop that visits its items. A for loop does that by assigning each item to a loop variable in list order. In this piece, I’ll show…

Matching each name with its score means using the values at the same positions in both lists. Python’s zip() lets a loop process values from corresponding positions together. I’ll show how to choose a loop for the information each pass…

len() on a list of ten million integers takes roughly 2.5 microseconds, while a Python loop over the same list takes roughly 300 milliseconds. The difference comes from a stored count rather than a faster algorithm, which decides the length…

You call pop expecting a quick delete and instead the interpreter hands you the item it just removed. That return is why mixing pop, remove and del leaves you with IndexError: pop from empty list or with None where a…

Python lists hold an ordered row of references you can read, change, and grow in place. I hit the classic alias surprise while verifying the samples for this page, I ran b = a followed by b.append(99) on Python 3.11.16…

A Python list comprehension builds a new list from an iterable in one expression. Put the output expression first, then the for clause, and add an if clause when items need filtering. Start with the smallest list comprehension Use a…