Strings, Lists, and Files

Name: Strings, Lists, and Files
Author: John Crabtree

Learn the different properties of strings, lists, and files and how to create them

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Course: On-Demand

By now you are quite familiar with the index operator and you know that you can use square brackets and specify an integer value that will enable you to access each character in the string. You can also start from the end of the string by using negative values. However, you can also create a sub string and you can do that with the slice operator. You simply use the name of the sequence, tell it where to start, where to end, and optionally, what the stride will be. And notice the delimiter here is a colon. And so you can print out the first three letters of our greeting by creating a start index value of zero and end of three. And that will produce a string that starts at zero and goes up to, but not including three, a sub string of length three. You can also leave off the beginning value if it is zero, zero will be assumed. Likewise, you can start from position three and go all the way to the end. That will be assumed. You can also begin with zero and go up to, but not including, the last character of the string, or up to, but not including the R. Now with the stride operator, you can print every other character if you wish, or every third character. So this is very flexible. And you do have to realize that a string is immutable. So if I have greeting, I can't change my mind and change the first letter to be an X by assignment. It will tell you that a string object does not support item assignment because it's immutable. So therefore if you have a sub string that you're interested in saving, then you need to assign that new object that's created with the slice operator into a new variable, that points to the new string that was just created. Now, this is very handy, can be used within a loop to do all kinds of interesting processing. And if you look at the loop that I have here, I'm taking the length of my string and I'm using that as the argument to range. So that will loop for each letter in that string. So let's try that out. So apparently I have 43 letters in this string, and I can choose to create all the possible sub strings of length three by simply using the slice where I start with index I and end with index I plus three.

Beginner Provider : John Crabtree 4 Lessons · 26m in Arabic, German, English, Spanish, French, Portuguese, Chinese

Course Description

These lessons begin with a demonstration of creating substrings using the slice operator. String methods and list methods are then presented and demonstrated with code. Finally, the module concludes with examples of how to read from and write to files.

LEARNING OBJECTIVES:

What You'll Learn

Create substrings from original strings using the start:end:stride slicing operation
Apply string methods and list methods through demonstrated code examples
Distinguish between immutable strings and mutable lists
Use the Python Standard Library and the built-in help function, including their benefits and limitations
Create and print lists using different methods
Read from and write to files, including using the append mode

Key Takeaways

Substrings can be created from original strings using the start:end:stride slicing operator.
Strings are immutable while lists are not.
Unified Modeling Language (UML) is the common design language used by software professionals.
The Python Standard Library and the built-in help function each have benefits and limitations.
Files can be read and written using several methods, including the append mode.