Introduction to strings in python (Part 2)

stay Last article in , We learned to be in python in , adopt % as well as format Function to format the string , today , Let's continue to learn a new way ：f-string. yes Python3.6 A new string formatting method , It is said that the performance is better than the first two methods , The code also looks more concise .

f-string Use of formatted strings

• Replace variable in string
• Used in conjunction with string related functions

Simple usage display ：

name = 'xiaobo'
age = 23
height = 173
print(f"my name is {name},my age is {age}")
print(f"my name is {name.upper()},my age is {age+1}")
print(f'my height is {height:.2f}')
Output is as follows :
my name is xiaobo,my age is 23
my name is XIAOBO,my age is 24
my height is 173.00

In addition to some of the usage shown above , There are also some responsible uses , You can expand it yourself when doing formatted output .

Introduction to some common built-in functions of string

• len(): Find the string length

name = 'xiaobo'
print(len(name))

• count(): Count the number of times a character appears in the string

name = 'my name is xiaobo'
print(name.count('m'))
# Specify the number of occurrences of a character from a certain position , The specified position coordinates are from 0 Start
print(name.count('m', 0))
print(name.count('m', 0, 9))
The output is 2

• replace() String replacement function

name = 'abcdmmm'
print(name.replace('m', 'n'))
print(name.replace('m', 'n', 1)) # You can specify the number of times to replace
Output results ：
abcdnnn
abcdnmm

• split(): String splitting function , You can specify the number of divisions

uri = 'username=xiaobo&password=123456&pagesize=20&pagenum=2'
print(uri.split('&'))
print(uri.split('&',1))
Output is as follows :
['username=xiaobo', 'password=123456', 'pagesize=20', 'pagenum=2']
['username=xiaobo', 'password=123456&pagesize=20&pagenum=2']

• find() function ： Find the location of the substring in the string , You can also specify the start and end positions to find , If not found, it will return -1.

uri = 'username=xiaobo&password=123456&pagesize=20&pagenum=2'
print(uri.find('password'))
print(uri.find('password', 5, 10))
Output :
16
-1

• index()： Follow find() Function usage is similar to , It is also used to find the index position of a substring in the string , If you can't find it , Will report ValueError: substring not found wrong .
• strip(): Eliminate the spaces at the beginning and end of the string , Returns a new string
• join(): Returns a new string generated by concatenating elements in a sequence according to a specified character

a = ['a', 'b', 'c']
print(''.join(a))
print('-'.join(a))
Output :
abc
a-b-c

Some other string checking functions

# Check if the string starts with the specified string
print('Hello world'.startswith('He')) # True
# Check if the string ends with the specified string
print('how are you !'.endswith('!')) # True
# Returns a new string , title case , The remaining letters become lowercase
print('hEllO, WOrld!'.capitalize()) # Hello, world!
# Returns a new string , All words are capitalized , The rest of the letters are in lowercase
print('hEllO, WOrld!'.title()) # Hello,World