r grammar

Adding R or R to the front of the string can eliminate the function of all escape characters in the string (each symbol comma is programmed with ordinary characters)

str1 = r'C:\Users\name\test\demo.py'
print(str1)			# C:\Users\name\test\demo.py

String formatting

1. Format string

Syntax: String% containing format placeholder (data1, data2,...)

1) % s - string placeholder

%s can occupy any type of data

str1 = '%sxx' % 'you'
print(str1)			# You xx
str1 = '%s-xxx' % [10, 20]
print(str1)			# [10, 20]-xxx

2) % d - integer placeholder

%d any digital data can be occupied

str1 = '%d-xxx' % 23
print(str1)			# 23-xxx

str1 = '%d-xxx' % 12.5
print(str1)			# 12-xxx

3) % f - floating point placeholder (six decimal places)

%f can occupy any digital data

str1 = '%fxx' % 4.34
print(str1)         # 4.340000xx

str1 = 'balance:%.2f' % 3452233.1515
print(str1)         # Balance: 345223.15

2.f-string

1. Syntax: f '{any resulting expression}' - fill the position of {} with the result of the expression
2. Add parameter
   • . Nf - controls the number of decimal places
   • , - Bank amount separated form
   • . n% - convert the number to percentage, and keep N decimal places for the ratio
   • x > N: convert the data into a string of length N. if it is not enough, fill it with the character corresponding to x in front
   • x < N: convert the data into a string of length N. if not enough, fill it with the character corresponding to x

1) Basic usage

str1 = f'{name}-{age}-{age * 10}-{name[-1]}'
print(str1)         # Xiaoming-18-180-ming

2) Parameters

a. .Nf

money = 2305
str1 = f'amount of money:{money:.2f}'
print(str1)         # Amount: 2305.00

b. ,

money = 2349000
str1 = f'Balance:{money:,}'
print(str1)			# Balance: 2349000

c. .N%

rate = 0.5
str1 = f'Duration occupancy:{rate:.2%}'
print(str1)			# Duration occupancy: 50.00%

d. x > N x < N

<, > - decide whether to fill in the front or the back

x - fill character

N - target length

num = 9
str1 = f'Python2106{num:0>3}'
print(str1)			# Python2106009

str1 = f'Python2106{num:0<3}'
print(str1)			# Python2106900

correlation function

1.center,rjust,ljust,zfill

• String. Center (len gt h, padding character), for example: 'abc'. center(7, 'x') – > 'xxabcxx'
• String. Rjust (len gt h, padding character), for example: 'abc'. rjust(7, 'x') – > 'xxxabc'
• String. Ljust (len gt h, padding character), for example: 'abc'. ljust(7, 'x') – > 'abcxxxx'
• String. Zfill (length) = = string. Rjust (length '0'), e.g. 'ABC'. zfill(7) – > '0000abc'

print('abc'.center(7, 'x'))			# xxabcxx
print('abc'.rjust(7, 'x'))			# xxxxabc
print('abc'.ljust(7, 'x'))			# abcxxxx
print('abc'.zfill(7))				# 0000abc

2.count

• String 1. Count (string 2) - counts the number of occurrences of string 2 in string 1
• String 1. Count (string 2, start subscript, end subscript): counts the number of occurrences of string 2 in the range from the start subscript to the end subscript (not available) in string 1

str1 = 'how are you? u am fine, thank you! and you?'
print(str1.count('a'))          # 4
print(str1.count('you'))        # 3

print(str1.count('a', 0, 12))   # 1

3.find/rfind,index/rindex

• String 1. Find (string 2) - get the first occurrence position of string 2 in string 1, and return the subscript value starting from 0; Returns - 1 if string 2 does not exist
• String 1. Index (string 2) - get the first occurrence position of string 2 in string 1, and return the subscript value starting from 0; If string 2 does not exist, an error is reported
• String 1.find (string 2, start subscript, end subscript), string 1.find (string 2, start subscript, end subscript)

str1 = 'how are you? i am fine, thank you! and you?'
str1 = 'how are you? i am fine, thank you! and you?'
print(str1.find('you'))         # 8
print(str1.rfind('you'))        # 39
print(str1.index('you'))        # 8
print(str1.rindex('you'))       # 39

print(str1.find('you1'))        # -1
# print(str1.index('you1'))     # report errors

print(str1.find('a', 4, 12))	# 4
print(str1.index('y', 3, 25))	# 8

4.isdigit(),isnumeric()

• String. isdigit() - judge whether it is a pure numeric string (numbers refer to numeric characters from 0 to 9)
• String. isnumeric() - judge whether it is a pure numeric string (a number is a character with numeric meaning)

print('234234'.isdigit())		# True
print('234234'.isnumeric())		# True
print('23 One million twelve⑤'.isnumeric())		# True

5.islower,isupper

• String. islower() - determines whether the string is a pure lowercase character string
• String. upper() - determines whether the string is a pure uppercase string

print('asda'.islower())			# True
print('SFAF'.isupper())			# True

6.join

• String. Join (sequence) - splices the elements in the sequence into a new string with the specified string

Note: the elements in the sequence must be strings

result = '+'.join('abc')
print(result)			# a+b+c

result = '+'.join(['name', 'Xiao Ming'])
print(result)			# name + Xiao Ming

result = ''.join(['name', 'Xiao Ming'])
print(result)			# name Xiaoming

Exercise: combine the elements in the list into a string

['abc', 100, 12.5, True, 'hello'] -> 'abc10012.5Truehello'

list1 = ['abc', 100, 12.5, True, 'hello'] 
result = ''.join([str(i) for i in list1])	# abc10012.5Truehello

Exercise 2: the scores of multiple students have been saved in a list. Extract the names of all students and return them as a string

[{name ':' Zhang San ',' age ': 18}, {name':'xiaoming ',' age ': 20}, {name':'xiaohua ',' age ': 30}] - >' Zhang San, Xiaoming, Xiaohua '

list1 = [{'name':'Zhang San', 'age': 18}, {'name':'Xiao Ming', 'age': 20}, {'name':'floret', 'age': 30}]
result = ','.join([str(stu['name']) for stu in list1])	# Zhang San, Xiao Ming, Xiao Hua

7.strip,lstrip,rstrip

• String. strip() - remove white space characters at both ends of the string
• String. lstrip() - remove the white space character in front of the string
• String. rstrip() - remove the white space characters after the string

str1 = '   \tabc i 123         \n'
result = str1.strip()
print('==', result, '===', sep='')

result = str1.lstrip()
print('==', result, '===', sep='')

result = str1.rstrip()
print('==', result, '===', sep='')

8.replace

• String 1. Replace (string 2, string 3) - replaces all string 2 in string 1 with string 3
• String 1. Replace (string 2, string 3, N) - replaces the first N string 2 in string 1 with string 3

str1 = 'how are you? i am fine, thank you! and you?'
result = str1.replace('u', 'b', 2)
print(result)           # how are yob? i am fine, thank yob! and you?

9.maketrans,translate

Str.maketrans (string 1, string 2) - create a character correspondence table for string 1 and string 2

table = str.maketrans('ain', 'You me him')     # a - you, i - me, n - him
result = str1.translate(table)
print(result)       # how you re you? I you m f I he e, th you he k you! You him d you?

Exercise: replace all Arabic numerals in the string with corresponding Chinese numerals

'123 wooden man, 88' - > '123 wooden man, 88'

table = str.maketrans('0123456789', 'zero one two three four five six seven eight nine')
str1 = '123 Wooden man, 88'
result = str1.translate(table)
print(result)			# One, two, three, eight

10.split

String 1.split (string 2) - cut the string using all string 2 in string 1 as the cut point

str1 = 'how are you? i am fine, thank you! and you?'
result = str1.split('you')
print(result)       # ['how are ', '? i am fine, thank ', '! and ', '?']

Note: if the cutting point is at the front or back, or there is a cutting point for practice, an empty string will appear

str2 = 'amnayouaa==a123aklpa'
print(str2.split())		# ['', 'mn', 'you', '', '==', '123', 'klp', '']