Let us step back a little. Before understanding your example, try to grok the example below for i in range(0, 3): print(i) which results in: 0 1 2 And the example below my_list = [42, 6, 2024] for i in range(0, 3): print(i, my_list[i]) Which results in: 0 42 1 6 2 2024 Are those clear to ya? Thanks! More on reddit.com

Well, let's break it down! words = [[str[0]]] This is written somewhat strangely, but basically it is setting the words variable to a list containing the first character of the string (note: this code should not use str as a variable name as this is also a type). for c in str[1:]: This for loop is going over the rest of the string character by character. This is called a slice, and essentially it cuts the list into index values. For example, if you had a list [1, 2, 3, 4, 5] and you indexed it with [2:3], the list you'd get back is [3, 4]. This is because you are slicing from index 2 (the third item since indexes start at 0) to index 3 (the 4th item). If you did [2:] instead, your list would be [3, 4, 5], as the empty value means "to the end of the list." If you reversed it with [:2] you'd instead get a list of [1, 2] because you are slicing from 0 (start) to 2. Note that [:2] and [0:2] are functionally the same. In the next section, you have words[-1][-1]. An index of [-1] means "the last element (length - 1). Any time you have a negative index in Python, it means "that many from the length." NOTE: a slice at the end must be blank if you want the last character. If you did [2:] and [2:-1] you'd get different values...in this case [3, 4, 5] and [3, 4] respectively. So what does the words[-1][-1] actually do? Well, remember that words is a list of characters. So you are looking at the last string and last letter of that string, then checking if it is lower case. The if also checks if the next letter is upper case. If it is, we append a new list of characters to the end of the words list. If not, we are instead appending the current character to the current list. This is repeated for the whole string. This list of lists is then converted into a list of individual strings by combining the internal lists into strings instead of a list of characters. You can tell what's going on if you put a print statement before the return. If I had a string, say, testWordOutput, the list before the returning list comprehension looks like this: [['t', 'e', 's', 't'], ['W', 'o', 'r', 'd'], ['O', 'u', 't', 'p', 'u', 't']]. This is actually a somewhat overcomplicated way to do this. You can skip the entire part where you create the internal lists, for example this code: def split_camel_case(original): if not original: # Early return for empty string return [] words = [original[0]] # Start with the first character for char in original[1:]: # If the current character is uppercase and # the previous character is lowercase, # start a new word if char.isupper() and words[-1][-1].islower(): words.append(char) else: # Otherwise, append the current character to the last word words[-1] += char return words This code does the exact same thing but is perhaps a bit more clear in how it works. It still has many of the same elements (the basic concept wasn't wrong) but removes the need for a list comprehension. Hopefully that makes sense, please let me know if you have questions. More on reddit.com

More time efficient than insert? why are you looking for such a thing? also why do you think such a thing exists? More on reddit.com

You can count backwards from the end like this. -1 is the last item, and -2 is the second to last item, etc. More on reddit.com