To join a list of DataFrames, say dfs, use the pandas.concat(dfs) function that merges an arbitrary number of DataFrames to a single one. When browsing StackOverflow, I recently stumbled upon the following interesting problem. By thinking about solutions to those small data science problems, you can improve your data science skills, so let’s dive into … Read more
To extract elements with specific indices from a Python list, use slicing list[start:stop:step]. If you cannot use slicing because there’s no pattern in the indices you want to access, use the list comprehension statement [lst[i] for i in indices], assuming your indices are stored in the variable indices. People always want to know the most … Read more
To convert a Python list to a NumPy array, use either of the following two methods: Exercise: Create array b from array a using both methods. Then change a value in array a. What happens at array b? NumPy vs Python Lists The Python built-in list data type is powerful. However, the NumPy array has … Read more
Q: What’s the object-oriented way to become wealthy? A: Inheritance. ? Your vocabulary determines the reality of your life. In this tutorial, I have compiled the most essential terms and concepts of object-oriented programming in Python. My goal was to create the best Python OOP cheat sheet that shows them in one place. Well — … Read more
To join specific list elements (e.g., with indices 0, 2, and 4) and return the joined string that’s the concatenation of all those, use the expression ”.join([lst[i] for i in [0, 2, 4]]). The list comprehension statement creates a list consisting of elements lst[0], lst[2], and lst[4]. The ”.join() method concatenates those elements using the … Read more
Slicing is a concept to carve out a substring from a given string. Use slicing notation s[start:stop:step] to access every step-th element starting from index start (included) and ending in index stop (excluded). All three arguments are optional, so you can skip them to use the default values (start=0, stop=len(lst), step=1). For example, the expression … Read more
To join and replace all strings in a list lst between start index 1 and end index 5, use the one-liner lst[1:5] = [”.join(lst[1:5])]. This solution is based on slice assignment that selects the slice you want to replace on the left and the values to replace it on the right side of the assignment. … Read more
Do you want to join a list of strings to a path in your specific operating system? Remembering the correct path separator can be a real pain. Fortunately, the os.path.join() method comes to the rescue! The os.path.join() method takes one or more path arguments and returns a concatenation of the path arguments with the correct … Read more
Given a list of strings. Join the first with the second string, the second with the third, and so on. The one-liner [lst[i] + lst[i+1] for i in range(0, len(lst), 2)] solves the problem by using the range function to iterate over every other index i=0, 2, 4, 5, … to concatenate the i-th and … Read more
What is the output of this code snippet? The string format function is a useful feature that is new in Python 3. Use it to programmatically insert variable values into the string. Without the format function, you must break the string into a series of smaller substrings and concatenate them. For example, the last line … Read more
🛑 Note: Python has zero-based indexing, i.e., the index of the first element is 0, and the index of the i-th element is (i-1). Not considering zero-based indexing but assuming the i-th element has index i is a common source of bugs! Here’s an example that demonstrates how list indexing works in Python: 🏃 Training … Read more
What is the output of this code snippet? You will use or have already used the operations introduced in this puzzle. They are elementary pieces of knowledge for any Python programmer. First, we have the two dictionaries mapping an account name to the number of followers. For example, Cristiano Ronaldo (key: “@cristiano”) has 120 million … Read more