Str Methods: Functions Inside of Objects

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Del curso dictado por University of Toronto

Learn to Program: The Fundamentals

1993 calificaciones

University of Toronto

Learn to Program: The Fundamentals

1993 calificaciones

Behind every mouse click and touch-screen tap, there is a computer program that makes things happen. This course introduces the fundamental building blocks of programming and teaches you how to write fun and useful programs using the Python language.

De la lección

For Loops and Fancy String Manipulation

This module introduces one way to repeat code (using a for loop), how to manipulate strings, and how to use a debugger to watch a program execute step by step.

More str Operators2:16

Str: Indexing and Slicing4:53

Str Methods: Functions Inside of Objects3:41

For Loop Over Str11:36

Conoce a los instructores

Jennifer Campbell
Associate Professor, Teaching Stream
Department of Computer Science
Paul Gries
Associate Professor, Teaching Stream
Department of Computer Science

So far, we have to find and use functions from within modules, for example module

Math contains functions that are related to Math such as square root and factorial.

It turns out that values, also known as objects, can contain functions as well,

functions inside of objects are called methods.

In this lecture, we'll explore string methods.

Here's a quick review. To use a function that has been defined

inside module Math,, we first import math which creates a variable called math that

refers to the module object that contains the various math functions.

And then to call one of these functions, we use that math variable.

We will do the same kind of thing to call string methods.

Here is a quote from Lewis Carroll's Alice in Wonderland.

We can get a new string that has all the uppercase letters replaced with their

lowercase equivalents by calling the lower method inside the white rabbit object.

This doesn't change the string that white rabbit refers to.

It produces a new string, so white rabbit still refers to the original string.

In order to find out which methods are available, we can use dir.

We can get the same answer if we use type stir, instead of variable, like rabbit.

We can ask for help on any of them. Return a copy of the string S converted to

lowercase. Let's look at the help for string method

count. Return the number of non overlapping

occurrences of substring sub in string S, starting in index start and going to index

end. These square brackets indicate optional

parameters. If I just say, string.count with one

argument, then it'll just look everywhere in the string.

Otherwise, it'll start at index start and go to index end.

We will use this to find out how many times the sub-string ate, a, t, e, appears

in the white rabbit quote. We can get a copy of a string with the

first letter capitalized. And if the string is already capitalized,

we just get back a copy of it. There is a method to find the index of the

first occurrence of a string inside another string.

We can specify a starting index. This asks for the first index of late that

starts at or after index seven. If the sub-string doesn't appear inside

the string, -one is returned, find is case sensitive.

There is an rfind method that searches for the last occurrence.

Rfind stands for right find Often, we want to remove spaces at the beginning or end

of a string. Method lstrip or left strip, returns a new

string but with the white space at the beginning removed.

Method rstrip operates at the right end. If we would like to remove white space

from both ends, we use the strip method. None of these modify the string that this

refers to. They all produce new strings.

This is the end of our whirlwind tour of strings and string methods.

We won't introduce every string method to you.

You can and should use dir and help to find out what other string methods exist.

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