An inventory often needs a quick way to find the quantity attached to a product name. Python dicts map keys to values, while sets hold distinct values for membership checks. I’ll explain how to choose between them and demonstrate dictionary…
A function like sorted() can take code you supply, such as a rule for how to compare items. A callback is a function you pass to another function, which then calls it while doing its work. In this piece, I’ll…
When the next calculation needs an array of zeros that lines up with an array you already have, NumPy can build it for you. np.zeros_like creates that array, copying the shape and data type of the one you give it.…
Data saved as a CSV (comma-separated values) file is plain text until you load it into something Python can work with. pandas read_csv() reads the file into a DataFrame, a table with labeled rows and columns. In this piece, I’ll…
`header=3` makes the fourth worksheet row the column labels. In the sample, `i20` becomes a heading, which makes me notice how directly that offset picks the labels. Compare a call for one worksheet with a call that uses `sheet_name=None`. Inspect…
I stacked two DataFrames with concat and watched every row line up wrong because the keys never matched. I ran pd.concat([employees, departments], axis=1) on my machine and got NaN-filled rows where Alice should have met Engineering, and that was when…
np.exp turns a large input into inf and only warns instead of raising an error. The overflow matters because it turns a softmax into NaNs, and the fix is one subtraction. What NumPy exp computes np.exp is a universal function,…
You are about to see a worked RSA example with p=61, q=53, the primes from the original 1977 RSA paper. The previous version of this article used p=3, q=7 and got d=5.0, which only decrypts by coincidence. The fixed version…
The first time I had to parse a timestamp from an API, I spent twenty minutes reaching for third-party libraries before remembering Python ships with exactly what I need. The datetime module is part of the standard library — no…
In this tutorial, I am going to demonstrate the different methods that you can use to get the cartesian product of a series of lists. You will learn 3 methods to find the cartesian product of a series of lists.…
