How do you find the index at the end of a string in python?
###Introduction Show The Python string data type is a sequence made up of one or more individual characters that could consist of letters, numbers, whitespace characters, or symbols. Because a string is a sequence, it can be accessed in the same ways that other sequence-based data types are, through indexing and slicing. This tutorial will guide you through accessing strings through indexing, slicing them through their character sequences, and go over some counting and character location methods. PrerequisitesYou should have Python 3 installed and a programming environment set up on your computer or server. If you don’t have a programming environment set up, you can refer to the installation and setup guides for a local programming environment or for a programming environment on your server appropriate for your operating system (Ubuntu, CentOS, Debian, etc.) ##How Strings are Indexed Like the list data type that has items that correspond to an index number, each of a string’s characters also correspond to an index number, starting with the index number 0. For the string
As you can see, the first We also notice that the whitespace character between The exclamation point ( The fact that each character in a Python string has a corresponding index number allows us to access and manipulate strings in the same ways we can with other sequential data types. ##Accessing Characters by Positive Index Number By referencing index numbers, we can isolate one of the characters in a string. We do this by putting the index numbers in square brackets. Let’s declare a string, print it, and call the index number in square brackets: Info: To follow along with the example code in this tutorial, open a Python interactive shell on your local system by running the
When we refer to a particular index number of a string, Python returns the character that is in that position. Since the letter Index numbers allow us to access specific characters within a string. ##Accessing Characters by Negative Index Number If we have a long string and we want to pinpoint an item towards the end, we can also count backwards from the end of the string, starting at the index number For the same string
By using negative index numbers, we can print out the character
Using negative index numbers can be advantageous for isolating a single character towards the end of a long string. ##Slicing Strings We can also call out a range of characters from the string. Say we would like to only print the word
When constructing a slice, as in When slicing strings,
we are creating a substring, which is essentially a string that exists within another string. When we call If we want to include either end of a string, we can omit one of the numbers in the
We did this by omitting the index number before the colon in the slice syntax, and only including the index number after the colon, which refers to the end of the substring. To print a substring that starts in the middle of a string and prints to the end, we can do so by including only the index number before the colon, like so:
By including only the index number before the colon and leaving the second index number out of the syntax, the substring will go from the character of the index number called to the end of the string. You can also use negative index numbers to slice a string. As we went through before, negative index numbers of a string start at -1, and count down from there until we reach the beginning of the string. When using negative index numbers, we’ll start with the lower number first as it occurs earlier in the string. Let’s use two negative index numbers to slice the string
The substring “ark” is printed from the string “Sammy Shark!” because the character “a” occurs at the -4 index number position, and the character “k” occurs before the -1 index number position. ##Specifying Stride while Slicing Strings String slicing can accept a third parameter in addition to two index numbers. The third parameter specifies the stride, which refers to how many characters to move forward after the first character is retrieved from the string. So far, we have omitted the stride parameter, and Python defaults to the stride of 1, so that every character between two index numbers is retrieved. Let’s review the example above that prints out the substring “Shark”:
We can obtain the same results by including a third parameter with a stride of 1:
So, a stride of 1 will take in every character between two index numbers of a slice. If we omit the stride parameter then Python will default with 1. If, instead, we increase the stride, we will see that characters are skipped:
Specifying the stride of 2 as the last parameter in the Python syntax Sammy Shark! Note that the whitespace character at index number 5 is also skipped with a stride of 2 specified. If we use a larger number for our stride parameter, we will have a significantly smaller substring:
Specifying
the stride of 4 as the last parameter in the Python syntax Sammy Shark! In this example the whitespace character is skipped as well. Since we are printing the whole string we can omit the two index numbers and keep the two colons within the syntax to achieve the same result:
Omitting the two index numbers and retaining colons will keep the whole string within range, while adding a final parameter for stride will specify the number of characters to skip. Additionally, you can indicate a negative numeric value for the stride, which we can use to print the original string in reverse order if we set the stride to -1:
The two colons without specified parameters will include all the characters from the original string, a stride of 1 will include every character without skipping, and negating that stride will reverse the order of the characters. Let’s do this again but with a stride of -2:
In this example, !krahS[whitespace]ymmaS The whitespace character is printed in this example. By specifying the third parameter of the Python slice syntax, you are indicating the stride of the substring that you are pulling from the original string. ##Counting Methods While we are thinking about the relevant index numbers that correspond to characters within strings, it is worth going through some of the methods that count strings or return index numbers. This can be useful for limiting the number of characters we would like to accept within a user-input form, or comparing strings. Like other sequential data types, strings can be counted through several methods. We’ll first look at the Let’s print the length of the string
The length of the string “Sammy Shark!” is 12 characters long, including the whitespace character and the exclamation point symbol. Instead of using a variable, we can also pass a string right into the
The If we want to count the number of times either one particular character or a sequence of characters shows up in a string, we can do so with the
We can search for another character:
Though the letter “S” is in the string, it is important to keep in mind that each character is case-sensitive. If we want to search for
all the letters in a string regardless of case, we can use the Let’s try
In the string We can also find at what position a character or character sequence occurs in a string. We can do this with the We can check to see where the first “m” occurs in the string
The first character “m” occurs at the index position of 2 in the string “Sammy Shark!” We can review the index number positions
of the string Let’s check to see where the first “likes” character sequence occurs in the string
The first instance of the character sequence “likes” begins at index number position 6, which is where the character What if we want to see where the
second sequence of “likes” begins? We can do that by passing a second parameter to the
In this second example that begins at the index number of 9, the first occurrence of the character sequence “likes” begins at index number 34. Additionally, we can specify an end to the range as a third parameter. Like slicing, we can do so by counting backwards using a negative index number:
This last example searches for the position of the sequence “likes” between the index numbers of 40 and -6. Since the final parameter entered is a negative number it will be counting from the end of the original string. The string methods of ##Conclusion Being able to call specific index numbers of strings, or a particular slice of a string gives us greater flexibility when working with this data type. Because strings, like lists and tuples, are a sequence-based data type, it can be accessed through indexing and slicing. You can read more about formatting strings and string methods to continue learning about strings. How do you index the end of a string?Strings are zero-indexed: The index of a string's first character is 0 , and the index of a string's last character is the length of the string minus 1.
How do you find the start and end index of a string in Python?Conclusion. Python 3.8. 1 is used.. str. find() , str. ... . str. index() , str. ... . re.search() — Returns None when a substring is not found.. str. find() , str,index() — Returns the lowest index of the substring.. str. ... . re.search() — Returns the match object that contains the starting and ending indices of the substring.. How do you do an end index in Python?What is this? To access the last element of a Python list, use the indexing notation list[-1] with negative index -1 which points to the last list element. To access the second-, third-, and fourth-last elements, use the indices -2 , -3 , and -4 .
How do you find the index of an element in a string Python?To find the index of a list element in Python, use the built-in index() method. To find the index of a character in a string, use the index() method on the string. This is the quick answer.
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