Python Tutorial column introduces strings.

A string or string (String) is a string of characters composed of numbers, letters, and underscores.

String

A string is a series of characters. In Python, everything enclosed in quotation marks is a string, and the quotation marks can be single quotation marks or double quotation marks, as shown below:

"This?is?a?string."???'This?is?also?a?string.'復(fù)制代碼

This flexibility allows you to Contains quotation marks and apostrophes:

'I?told?my?friend,?"Python?is?my?favorite?language!"'"The?language?'Python'?is?named?after?Monty?Python,?not?the?snake."?"One?of?Python's?strengths?is?its?perse?and?supportive?community."復(fù)制代碼

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Use method to modify the case of string

For strings, the most executable One of the simple things to do is to change the case of the words in it. Please look at the following code and try to judge its effect:

name?=?"fulade?blog"?print(name.title())復(fù)制代碼

Save this file as name.py, and then run it. You will see the following output:

Fulade?Blog復(fù)制代碼

In this example, the lowercase string "fulade blog" is stored in the variable name. In the print() statement, the method title() appears after this variable. In name.title(), the period (.) after name allows Python to perform the operation of method title() on the variable name. Each method is followed by a pair of parentheses because methods usually require some parameters to do their work. These parameters are often written in parentheses. The method title() does not require parameters, so the brackets after it are empty. The implementation result of title() is to display each word with the first letter capitalized, that is, change the first letter of each word to capitalized. There are several other useful ways to handle case. For example, to change a string to all uppercase or all lowercase, you can do as follows:

name?=?"Fulade?Blog"??print(name.upper())?
print(name.lower())復(fù)制代碼

The output is as follows:

FULADE?BLOG
fulade?blog復(fù)制代碼

Splicing string

In many cases, we need to merge strings. For example, you might want to store the first and last name in separate variables and then combine them into one when you want to display the name:

first_name?=?"Fu"last_name?=?"lade"full_name?=?first_name?+?"?"?+?last_name
print(full_name)復(fù)制代碼

Python uses the plus sign ( ) to combine strings. In this example, we use to combine first_name, spaces and last_name, to get the complete name, the result is as follows:

Fu?lade復(fù)制代碼

This method of merging strings is called splicing. Concatenation allows you to create a complete string from the strings stored in variables. Let's look at another example:

first_name?=?"fu"last_name?=?"lade"full_name?=?first_name?+?"?"?+?last_name
message?=?"Hello,?"?+?full_name.title()?+?"!"print(message)復(fù)制代碼

The above code displays the message "Hello, Fu Lade!", but stores this message in a variable, which makes the final print statement Much simpler.

Use tab characters (pressing the Tab key to generate spaces is called tab characters) or newline characters to add whitespace

In programming, whitespace generally refers to any non-printing characters such as spaces, tabs, and newlines. You can use whitespace to organize output and make it more readable. To add a tab character to a string, use the character combination \t, as shown in the following code:

print("Python")
Python
print("\tPython")
????Python復(fù)制代碼

To add a newline character to a string, use the character combination \n:

print("Languages:\nPython\nC\nJavaScript")?
Languages:
Python
C
JavaScript復(fù)制代碼

It is also possible to include both tab and newline characters in the same string. The string "\n\t" tells Python to wrap to the next line and Add a tab character to the beginning of the next line. The following example demonstrates how to use a single-line string to generate four lines of output: confuse. To a programmer,

and 'python ' look almost the same, but to a compiler, they are two different strings. Python is able to detect extra whitespace in 'python' and assume it is meaningful - unless you tell it otherwise. Whitespace is important because you often need to compare two strings to see if they are identical. For example, when a user logs in to the website, we need to compare the username. But in some scenarios we don't want spaces. Therefore, Python provides a very simple method to remove spaces. Python can find extra whitespace at the beginning and end of strings. To ensure that there are no whitespaces at the end of the string, use the method

. <pre class="brush:php;toolbar:false">print(&quot;Languages:\n\tPython\n\tC\n\tJavaScript&quot;)? Languages: ??Python ??C? ??JavaScript復(fù)制代碼</pre>The string stored in variable favorite_language contains extra spaces at the end. When you run this code, you can see the space at the end. After calling the method rstrip() on the variable

, this extra space is deleted. However, this deletion is only temporary. When you output the value of favorite_language again, you will find that the string is the same as when you entered it, still containing extra spaces. To permanently remove spaces from this string, the result of the removal operation must be saved back to a variable:<pre class="brush:php;toolbar:false">favorite_language?=?&quot;'python?'&quot;favorite_language?=?favorite_language.rstrip() print(favorite_language)'python'復(fù)制代碼</pre> <p>為刪除這個(gè)字符串中的空格，你需要將其末尾的空格剔除，再將結(jié)果存回到原來(lái)的變量中。 在我們的日常開(kāi)發(fā)中，經(jīng)常需要修改變量的值，再將新值存回到原來(lái)的變量中。 你還可以剔除字符串開(kāi)頭的空格，或同時(shí)剔除字符串兩端的空格。為此，可分別使用方法 <code>lstrip()和strip():

favorite_language?=?"'?python?'"?print(favorite_language.rstrip())'?python'print(favorite_language.lstrip())'python?'print(favorite_language.strip())'python'復(fù)制代碼

在這個(gè)示例中，我們首先創(chuàng)建了一個(gè)開(kāi)頭和末尾都有空格的字符串。接下來(lái)，我們 分別刪除末尾、開(kāi)頭兩端的空格。在實(shí)際程序開(kāi)發(fā)中，這些剔除函數(shù)最常用于在存儲(chǔ)用戶(hù)輸入前對(duì)輸入進(jìn)行清理。

使用字符串時(shí)避免語(yǔ)法錯(cuò)誤

語(yǔ)法錯(cuò)誤是一種經(jīng)常會(huì)出現(xiàn)的錯(cuò)誤。程序中包含非法的Python代碼時(shí)，就會(huì)導(dǎo)致語(yǔ)法錯(cuò)誤。 例如，在用單引號(hào)括起的字符串中，如果包含撇號(hào)，就將導(dǎo)致錯(cuò)誤。這是因?yàn)檫@會(huì)導(dǎo)致Python將 第一個(gè)單引號(hào)和撇號(hào)之間的內(nèi)容視為一個(gè)字符串，進(jìn)而將余下的文本視為Python代碼，從而引發(fā) 錯(cuò)誤。 下面演示了如何正確地使用單引號(hào)和雙引號(hào)。

message?=?"One?of?Python's?strengths?is?its?perse?community."?print(message)復(fù)制代碼

撇號(hào)位于兩個(gè)雙引號(hào)之間，因此Python解釋器能夠正確地理解這個(gè)字符串:

One?of?Python's?strengths?is?its?perse?community.復(fù)制代碼

然而，如果你使用單引號(hào)，Python將無(wú)法正確地確定字符串的結(jié)束位置:

message?=?'One?of?Python's?strengths?is?its?perse?community.'
print(message)復(fù)制代碼

而你將看到如下輸出:

message?=?'One?of?Python's?strengths?is?its?perse?community.'
SyntaxError:?invalid?syntax復(fù)制代碼

從上面的輸出我們可以看到，錯(cuò)誤發(fā)生在第二個(gè)單引號(hào)后面。這種語(yǔ)法錯(cuò)誤表明，在解釋器看來(lái)，其中的有些內(nèi)容不是有效的Python代碼。錯(cuò)誤的來(lái)源多種多樣，這里指出一些常見(jiàn)的。學(xué)習(xí) 編寫(xiě)Python代碼時(shí)，你可能會(huì)經(jīng)常遇到語(yǔ)法錯(cuò)誤。

所以，大家在做練習(xí)的時(shí)候也要細(xì)心，避免出現(xiàn)這種小錯(cuò)誤。

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