Python3 String

Strings are the most commonly used data type in Python. We can use quotation marks ( ' or " ) to create strings.

Creating a string is easy, just assign a value to the variable. E.g:

var1 = 'Hello World!'
var2 = "TutorialFish"

Python Access Value in String

Python does not support single-character types, and single-characters are also used as a string in Python.

When Python accesses substrings, you can use square brackets [ ] to intercept strings. The syntax format of string interception is as follows:

variable [head index: tail index]

The index value starts with 0 , and -1 is the starting position from the end.

str = "TRY IT"
str[0] = 'T'
str[1] = 'R'
str[2] = 'Y'
str[3] = ' '
str[4] = 'I'
str[5] = 'T'
str[:] = 'TRY IT'
str[0:] = 'TRY IT'
str[:6] = 'TRY IT'
str[:3] = 'TRY'
str[0:2] = 'TR'
str[1:4] = 'RY '

Examples are as follows:

Examples (Python 3+)

#!/usr/bin/python3
 
var1 = 'Hello World!'
var2 = "Try It"
 
print ("var1[0]: ", var1[0])
print ("var2[1:5]: ", var2[1:5])

Execution results of the above examples:

var1[0]:  Hvar2[1:5]:  ry I

Python String Update

You can intercept a part of the string and concatenate it with other fields, as in the following example:

Examples (Python 3+)

#!/usr/bin/python3

var1 = 'Hello World!'

print("Updated string: ", var1[:6] + 'TutorialFish!')

Execution results of the above examples

Updated string:  Hello TutorialFish!

Python Escape Characters

When you need to use special characters in characters, Python uses backslash \ to escape characters. The following table:

>>> print("line1 \
... line2 \
... line3")
line1 line2 line3
>>>

>>> print("\\")\

>>> print('\'')'

>>> print("\"")"

>>> print("\a")

>>> print("Hello \b World!")
Hello World!

>>> print("\000")
>>>

>>> print("\n")
>>>

>>> print("Hello \v World!")
Hello        World!
>>>

>>> print("Hello \t World!")
Hello      World!>>>

>>> print("Hello\rWorld!")
World!
>>> print('google tutorialfish bing\r123456')
123456 tutorialfish bing

>>> print("Hello \f World!")
Hello        World!
>>>

>>> print("\110\145\154\154\157\40\127\157\162\154\144\41")
Hello World!

>>> print("\x48\x65\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21")
Hello World!

Python String Operators

In the following table, the value of the variable a is the string "Hello", and the value of the b variable is "Python":

print(r '\n')
print(R '\n')

Examples (Python 3+)

#!/usr/bin/python3

a = "Hello"
b = "Python"

print("a + b output result:", a + b)
print("a * 2 output result:", a * 2)
print("a[1] output result:", a[1])
print("a[1:4] output result:", a[1:4])

if("H" in a):
    print("H in variable a")
else:
    print("H is not in variable a")

if("M" not in a):
    print("M is not in variable a")
else:
    print("M is in variable a")
    
print(r'\n')
print(R'\n')

The output of the above example is:

a + b output result: HelloPythona * 2 output result: HelloHelloa[1] output result: ea[1:4] output result: ellH in variable aM is not in variable a\n\n

Python String Formatting

Python supports the output of formatted strings. Although very complex expressions may be used in this way, the most basic usage is to insert a value into a string with the string format character %s.

In Python, string formatting uses the same syntax as the sprintf function in C.

Example (Python 3+)

#!/usr/bin/python3
print("My name is %s %d years old this year!" % ('Jake', 10))

The output of the above example:

My name is Jake 10 years old this year!

Python string formatting symbols:

Format operator auxiliary instructions:

Starting from Python2.6, a new function str.format() has been added for formatting strings, which enhances the function of string formatting.

Python Triple Quotes

Python triple quotation marks allow a string to span multiple lines, and the string can contain line breaks, tabs, and other special characters. Examples are as follows:

Examples (Python 3+)

#!/usr/bin/python3
 
para_str = """This is an example of a multi-line string
Multi-line strings can use tabs
TAB (\t ).
You can also use the newline character [\n ].
"""
print (para_str)

The execution result of the above example is:

This is an example of a multi-line stringMulti-line strings can use tabsTAB (    ).You can also use the newline character [ ].

The triple quotation marks free programmers from the quotation marks and special strings, keeping a small piece of string format throughout the so-called WYSIWYG (What You See Is What You Get) format.

A typical use case is when you need a piece of HTML or SQL, then use string combination, special string escape will be very cumbersome.

errHTML = '''
<HTML><HEAD><TITLE>
Friends CGI Demo</TITLE></HEAD>
<BODY><H3>ERROR</H3>
<B>%s</B><P>
<FORM><INPUT TYPE=button VALUE=Back
ONCLICK="window.history.back()"></FORM>
</BODY></HTML>
'''

cursor.execute('''
CREATE TABLE users (  
login VARCHAR(8), 
uid INTEGER,
prid INTEGER)
''')

f-string

f-string was added after python3.6. It is called a literal format string, which is the syntax of a new format string.

We used to use percent signs (%) before:

Example

>>> name = 'TutorialFish'
>>> 'Hello %s' % name
'Hello TutorialFish'

The f-string format string starts with f and is followed by a string. The expression in the string is wrapped in curly braces {}, which will replace the calculated value of the variable or expression. Examples are as follows:

Example

>>> name ='TutorialFish'
>>> f'Hello {name}' # Replace variable
'Hello TutorialFish'
>>> f'{1+2}' # Use expression
'3'

>>> w = {'name': 'TutorialFish', 'url': 'www.tutorialfish.com'}
>>> f'{w["name"]}: {w["url"]}'
'TutorialFish: www.tutorialfish.com'

In this way, it is obviously simpler, and there is no need to judge whether to use %s or %d.

In the Python 3.8 version, the = symbol can be used to concatenate operation expressions and results:

Example

>>> x = 1
>>> print(f'{x+1}')   # Python 3.6
2

>>> x = 1
>>> print(f'{x+1=}')   # Python 3.8
x+1=2

Unicode String

In Python2, ordinary strings are stored as 8-bit ASCII codes, while Unicode strings are stored as 16-bit unicode strings, which can represent more character sets. The syntax used is to prefix the string with u .

In Python3, all strings are Unicode strings.

Python String Built-In Functions

Python's string commonly used built-in functions are as follows: