![]() The slice object initialization takes in 3 arguments with the last one being the optional index increment. There are objects in Python called slice objects and the can be used in place of the colon syntax above. There is another form of syntax you can use that may be easier to understand. I'll give an example just to illustrate that it's indeed the same. The exact same syntax and the exact same way of doing things. Slicing Python TuplesĮverything above also works for tuples. If you wanted the even indexes going backwards, you could skip every second element and set the iteration to -2. And that -1 I snuck in at the end? It means to increment the index every time by -1, meaning it will traverse the list by going backwards. This saves us time so that we don't have to manually specify len(a) as the ending index. If there isn't a value after the first colon, it means to go all the way to the end of the list. If there is no value before the first colon, it means to start at the beginning index of the list. Lists have a default bit of functionality when slicing. Python Slicing (Lists, Tuples and Arrays) in ReverseĪlright, how about if we wanted our list to be backwards, just for the fun of it? Let's try something crazy. By default, Python sets this increment to 1, but that extra colon at the end of the numbers allows us to specify what we want it to be. That last colon tells Python that we'd like to choose our slicing increment. In the example above, say that we did not want that ugly 3 returned and we only want nice, even numbers in our list. There is also an optional second clause that we can add that allows us to set how the list's index will increment between the indexes that we've set. Advanced Python Slicing (Lists, Tuples and Arrays) Increments The colon in the middle is how Python's lists recognize that we want to use slicing to get objects in the list. The 4 means to end at the fifth element in the list, but not include it. The 1 means to start at second element in the list (note that the slicing index starts at 0). What the heck does that syntax mean? Good question. Here's the Pythonic way of doing things: Now let's say that we really want the sub-elements 2, 3, and 4 returned in a new list. Nothing crazy, just a normal list with the numbers 1 through 8. Let's start with a normal, everyday list. Slicing Python Lists/Arrays and Tuples Syntax The default increment is 1, but users can put any applicable positive integer in step. It is an integer value that indicates to Python how much the user wants to increment between indexes when slicing the list. The last parameter that Python accepts is called step, and it can be entered optionally as required. In other words, if the stop value is 5 when using the slice function, Python will only return values till the index value is 4. By default, Python will stop the slicing at the value “stop - 1.” On the other hand, entering the stop parameter is mandatory since it indicates to Python the index to which slicing is supposed to take place. The value of start defaults to None if no value is provided. The start parameter is optional and indicates the index of the container which you want to begin slicing the data type from. The slice function accepts up to three parameters at the same time. Using negative indexes, Python users can access the data in a data type from the end of the container rather than the beginning. ![]() Python also uses the concept of negative indexes to make data easier to access. Regardless of what data the data type is holding, index values always begin at zero and end at one less than the number of items in the list. The “index” of a character or element in a list-like data type is the position of the character or element in the data type. This is because Python uses the concept of indices in all of them. You can use the slice function with several different data types in Python – including lists, tuples, and strings. To understand how the slice function works in Python, it’s necessary for you to understand what an index is. Slicing can not only be used for lists, tuples or arrays, but custom data structures as well, with the slice object, which will be used later on in this article. Python has an amazing feature just for that called slicing. So you've got an list, tuple or array and you want to get specific sets of sub-elements from it, without any long, drawn out for loops? ![]()
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