Read a List of Words From Stdin in Java and Store Those Words in an List

So we've seen numbers, just what about text? This page is about the Python string, which is the go-to Python data type for storing and using text in Python. And so, in Python, a piece of text is chosen a cord and yous can perform all kinds of operations on a cord. But let'due south start with the basics starting time!

• What is a Python cord?
• How to create a Python string
• Unmarried or double quotes?
• Multiline strings
• String operations
• Python string format with f-strings

What is a Python string?

The following is a formal definition of what a string is:

String

A string in Python is a sequence of characters

In even simpler terms, a string is a piece of text. Strings are not just a Python thing. Information technology'due south a well-known term in the field of information science and ways the same matter in near other languages as well. Now that we know what a cord is, we'll wait at how to create a cord.

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How to create a Python string

A Python string needs quotes around it for it to be recognized as such, like this:

>>> 'Hello, World' 'Hello, Globe'

Because of the quotes, Python understands this is a sequence of characters and not a command, number, or variable.

And just like with numbers, some of the operators we learned earlier work on Python strings likewise. Try it with the following expressions:

>>> 'a' + 'b' 'ab' >>> 'ab' * 4 'abababab' >>> 'a' - 'b' Traceback (most recent call concluding):   File "<stdin>", line 1, in <module> TypeError: unsupported operand type(s) for -: 'str' and 'str'

This is what happens in the code above:

• The plus operator glues two Python strings together.
• The multiplication operator repeats our Python cord the given number of times.
• The minus operator doesn't work on a Python string and produces an error. If y'all desire to remove parts of a cord, at that place are other methods that you'll learn about later on.

Single or double quotes?

We've used single quotes, just Python accepts double-quotes effectually a cord besides:

>>> "a" + "b" 'ab'

Note that these are not two single quotes adjacent to each other. It's the character that'due south often constitute next to the enter central on your keyboard. You demand to printing shift together with this key to go a double quote.

Equally you can see from its answer, Python itself seems to adopt unmarried quotes. It looks more clear, and Python tries to exist equally articulate and well readable as it tin can. And then why does it support both? It's considering it allows you lot to use strings that comprise a quote.

In the first example beneath, nosotros use double quotes. Hence in that location's no problem with the single quote in the word information technology'southward. Nevertheless, in the second example, we try to use single quotes. Python sees the quote in the word it'due south and thinks this is the cease of the string! The following alphabetic character, "south", causes a syntax error. A syntax error is a character or string incorrectly placed in a command or instruction that causes a failure in execution.

In other words, Python doesn't sympathise the s at that spot, considering it expects the string to exist concluded already, and fails with an error:

>>> mystring = "Information technology's a string, with a single quote!" >>> mystring = 'Information technology's a cord, with a single quote!'   File "<stdin>", line 1     mystring = 'It's a string, with a single quote!'                    ^ SyntaxError: invalid syntax

As you tin can meet, even the syntax highlighter on the code cake above gets confused! And equally you lot can also see, Python points out the verbal location of where it encountered the error. Python errors tend to exist very helpful, then await closely at them and you'll often be able to pinpoint what'due south going wrong.

Escaping

In that location's actually another way around this problem, chosen escaping. Yous can escape a special character, similar a quote, with a backward slash:

>>> mystring = 'It\'due south an escaped quote!' >>> mystring "It'south an escaped quote!"

Y'all tin also escape double quotes inside a double-quoted cord:

>>> mystring = "I'm a so-called \"script kiddie\"" >>> mystring 'I\'m a so-called "script kiddie"'

Here, over again, you encounter Python's preference for unmarried quotes strings. Even though nosotros used double quotes, Python echos the string back to u.s.a. using unmarried quotes. It'southward still the aforementioned string though, it's simply represented differently. Once you lot start printing strings to the screen, you'll see the evidence of this.

So which one should you apply? Information technology's uncomplicated: always opt for the option in which you need the least amount of escapes considering these escapes make your Python strings less readable.

Multiline strings

Python as well has syntax for creating multiline strings, using triple quotes. Past this I mean 3 double quotes or iii single quotes, both work but I'll demonstrate with double quotes:

>>> my_big_string = """This is line i, ... this is line 2, ... this is line three."""

The squeamish thing here is that you tin utilize both single and double quotes within a multiline string. So you lot tin can use triple quotes to cleanly create strings that contain both single and double quotes:

>>> line = """He said: "Hello, I've got a question" from the audition"""

String operations

Strings come up with a number of handy, congenital-in operations you tin execute. I'll show you only a couple hither since I don't want to divert your attention from the tutorial too much.

In the REPL, you can utilize car-completion. In the next code fragment, we create a string, mystring, and on the next line we blazon its name followed by hitting the <TAB> key twice:

>>> mystring = "Hello world" >>> mystring. mystring.capitalize(    mystring.find(          mystring.isdecimal(     mystring.istitle(       mystring.sectionalisation(     mystring.rstrip(        mystring.translate( mystring.casefold(      mystring.format(        mystring.isdigit(       mystring.isupper(       mystring.replace(       mystring.split(         mystring.upper( mystring.center(        mystring.format_map(    mystring.isidentifier(  mystring.bring together(          mystring.rfind(         mystring.splitlines(    mystring.zfill( mystring.count(         mystring.index(         mystring.islower(       mystring.ljust(         mystring.rindex(        mystring.startswith( mystring.encode(        mystring.isalnum(       mystring.isnumeric(     mystring.lower(         mystring.rjust(         mystring.strip( mystring.endswith(      mystring.isalpha(       mystring.isprintable(   mystring.lstrip(        mystring.rpartition(    mystring.swapcase( mystring.expandtabs(    mystring.isascii(       mystring.isspace(       mystring.maketrans(     mystring.rsplit(        mystring.title(

If all went well, y'all should get a big list of operations that tin be performed on a cord. You can try some of these yourself:

>>> mystring.lower() 'hello world' >>> mystring.upper() 'HELLO WORLD'

An explanation of each of these operations can be found in the official Python documentation, but we'll comprehend a few here too.

Getting the cord length

A mutual operation is to go the string length. Unlike the operations higher up, this can be done with Python's len() role like this:

>>> len("I wonder how long this string will be...") twoscore >>> len(mystring) eleven

In fact, the len() function can exist used on many objects in Python, as you lot'll acquire later on on. If functions are new to you, yous're in luck, because our next page volition explain exactly what a function in Python is, and how yous can create one yourself.

Split a string

Another common operation is splitting a string. For this, we can apply one of the built-in operations, conveniently chosen split. Let's start simple, past splitting upward two words on the infinite character betwixt them:

'Hello globe'.split(' ') ['Hi', 'earth']

The split functioning takes one argument, which is the sequence of characters to split up on. The output is a Python list, containing all the separate words.

Carve up on whitespace

A common use-case is to dissever on whitespace. The problem is that whitespace tin can exist a lot of things. Three mutual ones that you probably know already are:

• space characters
• tabs
• newlines

But in that location are many more than, and to make it even more complicated, whitespace doesn't mean just i of these characters, just tin likewise exist a whole sequence of them. E.k., three consecutive spaces and a tab grapheme course i slice of whitespace.

Exactly because this is such a common operation among programmers, and because it'due south hard to do information technology perfectly, Python has a user-friendly shortcut for it. Calling the split performance without whatsoever arguments splits a cord on whitespace, as tin can be seen beneath:

>>> 'Howdy \t\due north there,\t\t\t stranger.'.split() ['Hello', 'there,', 'stranger.']

Equally you can see, no matter what whitespace character and how many, Python is still able to separate this string for us into separate words.

Supersede parts of a string

Let'southward look at ane more than congenital-in performance on strings: the supervene upon function. It'due south used to supersede one or more than characters or sequences of characters:

>>> 'Hi world'.replace('H', 'h') 'hello earth' >>> 'Hello world'.replace('l', '_') 'He__o wor_d >>> 'Hi earth'.replace('earth', 'readers') 'Howdy readers'

Reversing a cord

A mutual consignment is to reverse a Python string. There'southward no opposite operation, though, every bit you might have noticed when studying the list of operations like lower() and upper() that comes with a string. This is not exactly beginner stuff, and so experience free to skip this for now if you're going through the tutorial sequentially.

To reverse a string efficiently, we can care for a string as a list. Lists are covered later on in this tutorial (see for-loop). In fact, you lot could run into a cord every bit a list of characters. And, more chiefly, you can care for information technology equally such. List index operations similar mystring[2] work merely like they work on lists:

>>> mystring = 'How-do-you-do globe' >>> mystring[ii] '50' >>> mystring[0] 'H'

Note that in Python, like in all figurer languages, we start counting from 0.

What besides works exactly the same equally in lists, is the slicing operator. Details of list slicing can exist found on the Python list folio and won't be repeated here. If you're coming from other languages, yous might compare it to an operation like substring() in Coffee, which allows y'all to call up specific parts of a string.

Slicing in Python works with the slicing operator, which looks like this: mystring[start:stop:step_size]. The key characteristic we utilise from slicing is the stride size. By giving the slicing operator a negative stride size of -i, nosotros traverse the string from end to beginning. By leaving the start and terminate position empty, Python assumes with want to slice the entire string.

Then we can employ slicing to reverse a Python cord as follows:

>>> mystring = 'Hello world' >>> mystring[::-1] 'dlrow olleH'

Python string format with f-strings

A mutual pattern is the need to merge some text strings together or use a variable inside your cord. At that place are several ways to practice so, but the most modern manner is to use f-strings, curt for formatted strings.

Let'south outset wait at an instance, earlier we dive into the details:

>>> my_age = 40 >>> f'My age is {my_age}' My age is forty

The f-string looks like a regular string with the improver of an f prefix. This f tells Python to scan the string for curly braces. Inside these curly braces, we can put whatsoever Python expression we want. In the higher up instance, nosotros just included the variable my_age. F-strings provide an elegant mode of including the results of expressions within strings.

Here are a couple more examples yous can try for yourself likewise, within the REPL:

>>> f'iii + 4 = {3+4}' 'iii + 4 = 7' >>> my_age = twoscore >>> f'My age is, unfortunately, not {my_age-8}' 'My age is, unfortunately, non 32'

I'thou just touching the nuts hither. If you lot're following the tutorial front to back, you can go on with the next topic since you know more than enough for now. If y'all'd like to find out more about f-strings, try the post-obit resources:

• Official docs on f-strings
• The official guide has some more examples here: formatted string literals

Thanks for reading my tutorials. I use ads to proceed writing free articles, I hope you lot understand! Support me by disabling your adblocker on my website or, alternatively, buy me a coffee.

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Source: https://python.land/introduction-to-python/strings

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