Standard-library directories and site-packages still appear in the example’s sys.path with PYTHONPATH unset. For me, the sharper surprise is the blank entry: it represents the current working directory for this -c invocation. Take an importable .py file as a concrete…
I love that sorted() returns a new list rather than rearranging the tuple in the example. By contrast, list.sort() rearranges mutable_values in the example and returns None. Assign the return value from sorted(values) to ordered. You can print or iterate…
Python picks (5, 8) over (5, 2). I value getting one winner without asking Python to order every candidate. When the candidates are records, you may need the winning object for its other fields. Follow max()’s result for a record…
Python’s range() hands back a range object instead of a list of numbers, and that single choice explains the stop value that causes off-by-one loops. The object stores three integers and works out each element when something asks for it,…
I kept typing 7 // 3 and expecting 3. I had just switched from a language where integer division truncates toward zero, so floor division felt like a bug until I ran the numbers. Once I traced the three ceiling…
Python stops on the line the moment it meets && inside an if statement, and the caret lands under the second ampersand. Every C-family language accepts those two characters for logical conjunction, so a parser error reads like a bug…
Print the result of the Python map function and you get an address instead of a list, because nothing has run yet. The four numbers you passed in are still waiting inside an iterator, and the values only appear when…
The first time I wrote an event handler in Python, I passed a function to another function and could not figure out why it worked. The function I passed was not executed immediately – it was stored and called later…
I keep coming back to the Python sum() function whenever I need a quick way to add up numbers. It is one of those built-in tools that seems simple on the surface but has enough quirks to trip you up…
I ran into a situation last year where I had a pandas DataFrame with 50 columns and needed to pull out specific columns by their numerical position. The column names were generated programmatically and I had no way to know…