python The most basic data types in are as follows ：
Number（ Numbers ）
String（ character string ）
List（ list ）
Tuple（ Tuples ）
Dictionary（ Dictionaries ）
One 、 String creation
String type ’str’ Is the most commonly used data type , You can use quotation marks （ Single or double quotation marks ） To create a string . There are two points to note ：
1. Single quotation marks and double quotation marks are essentially the same . But when the string contains single quotation marks , If you use a single quoted string , As a result, the single quotation mark in the string cannot be distinguished from the single quotation mark in the string , So use the escape string . If you use a double quoted string , Write single quotation marks directly in the string . Such as ：
‘abc”dd”abc’
“’acc’d’12”
2. A three quote string can consist of multiple lines , Single quote or double quote strings do not , When you need to use large, multi line strings , have access to . Such as ：
‘’’
Multiple string references
‘’’
stay python In the program , Characters in a string can include numbers 、 Letter 、 Chinese characters 、 Special symbols , And some invisible control characters , As a newline 、 Box drawings, etc .
Two 、 The subscript of a string str[beg:end]
str = 'hello world'
print(str[1]) # e Subscript from 0 Start
print(str[10]) # d
print(str[-1]) # d Take the last value
print(len(str))# 11
print(str[12]) # Report errors Transboundary , Out of range 3、 ... and 、 Slice of string ：slice(start, stop[, step])
str = 'hello world'
print(str [6:11:]) # world The range is semi closed and semi open [6:10)
print(str [::]) # hello world Take the whole string
print(str [::2]) # hlowrd Value based on step size , Step cannot be 0, Floating point numbers are not allowed
print(str [::-1])# dlrow olleh Output in reverse order
print(str [6:12:]) #world When taking a single character , If the index is out of range, an error will be reported . No error will be reported when slicing .Four 、 String formatting ：# %s—— character string ,%d—— Integers ,%f—— Floating point numbers
# String formatting
name = 'hansen'
age = 20
# % Data types need to be considered
print("%s The age is %d" %(name, age))#hansen The age is 20
print("{} The age is {}".format(name, age)) #hansen The age is 20 Order to be considered
print("{1} The age is {0}".format(age, name)) #hansen The age is 20 There is no need to consider the order , Consider indexing
print(f"{name} The age is {age}") #hansen The age is 205、 ... and 、 Common methods of string
S.find(sub) --> Returns the smallest index of the element S.index(sub) --> Returns the smallest index of the element
S.replace(old, new[, count]) --> Replace
S.split(sep=None) --> With sep To split the string , And return to the list .sep The default is None, The default split is space
S.startswith(prefix[, start[, end]]) --> Determine whether the string starts with a prefix , Return to bool value .
S.endswith(suffix[, start[, end]]) --> Determine whether a string ends with a suffix , Return to bool value .
S.lower() --> Convert all strings to lowercase
S.upper() --> Convert all strings to uppercase
S.strip([chars]) --> By default, the characters around the string are removed , Default is space
S.isalpha() --> Determine whether the string is all alphabetic , The return is bool value
S.isdigit() --> Determine whether the string is all numbers , The return is bool value
S.isalnum() --> Judge whether the string is all numbers or letters , There are no special characters , The return is bool value
S.join(iterable) --> The elements in the sequence are concatenated with the specified characters to produce a new string
