I. conversion between base numbers
- Example
Basic data types and built-in methods
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Integer int
Purpose: used to record the integer related status of people's age, mobile phone number, etc
Definition method: age = 18
Commonly used in mathematical calculation
Summary: int of integer type is out of order, immutable, and has a value
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Floating point
Purpose: to record the decimal related status of height, weight, salary, etc
Definition method: height = 1.77
Commonly used in mathematical calculation
Summary: unordered, immutable, one value
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String str
Purpose: to save some descriptive information, personal hobbies, personal profile
Definition method: S1 ='yafeng666 '
It can be expressed in single quotation mark, double quotation mark or triple quotation mark, but cannot be mixed
Summary: ordered, immutable, one value
The built-in method of string priority
#1.strip() removes the spaces on the left and right sides of the string, but it can't remove the middle space. That user is too unfriendly s1 = "***yafeng666***" s1.strip("*") print(s1.strip("*")) >>>yafeng666 #2.split() is used to segment strings. You can specify the separator of segmentation and return a list s2 = "yafeng|18|male" s2.split("|") print(s2.split("|")) >>>['yafeng', '18', 'male'] #3.len() gets the number of elements in the current data, and the space is also a character s1 = "***yafeng666***" print(len(s1)) >>>15 str1 = 'hello python!' # 4. Value by index (forward, reverse): # 4.1 forward direction (from left to right) >>> str1[6] p # 4.2 reverse fetching (negative sign means right to left) >>> str1[-4] h # 4.3 for str, the value can only be taken according to the index and cannot be changed >>> str1[0]='H' # Error TypeError # 5. Slice (look at the head and ignore the tail, step size) # 5.1 ignore head and tail: take out all characters with index from 0 to 8 >>> str1[0:9] hello pyt # 5.2 step size: 0:9:2, the third parameter 2 represents the step size, it will start from 0 and accumulate one 2 at a time, so the characters of index 0, 2, 4, 6 and 8 will be taken out >>> str1[0:9:2] hlopt # 5.3 reverse sectioning >>> str1[::-1] # -1 means right to left !nohtyp olleh # 6. Member operations in and not in # 6.1 int: judge whether hello is in str1 >>> 'hello' in str1 True # 6.2 not in: judge whether tony is not in str1 >>> 'tony' not in str1 True # 7. cycle >>> str5 = 'How are you today?' >>> for line in str5: # Extract each character in the string in turn ... print(line) ... //this //day //you //good //Do you ？
- Methods to master string
1,strip,lstrip,rstrip str1 = "***yafeng666***" >>> str1.strip('*') # Remove left and right specified characters 'yafeng666' >>> str1.lstrip('*') # Remove only the specified characters on the left yafeng666*** >>> str1.rstrip('*') # Remove only the specified characters on the right ***yafeng666 2,lower(),upper() >>> str2 = 'My nAme is yafenG!' >>> str2.lower() # Change all English strings to lowercase my name is yafeng! >>> str2.upper() # Capitalize all English strings MY NAME IS YAFENG! 3,startswith,endswith >>> str3 = 'yafeng 666' # Startswitch() determines whether the string starts with the character specified in parentheses, and the result is a Boolean value of True or False >>> str3.startswith('y') True >>> str3.startswith('j') False # Endswitch() determines whether the string ends with the character specified in parentheses, and the result is a Boolean value of True or False >>> str3.endswith('666') True >>> str3.endswith('sixsixsix') False 4,Format output format # Similar to the usage of% s, the passed in value will correspond to {} one by one according to the location >>> str4 = 'my name is {}, my age is {}!'.format('yafeng', 18) >>> str4 my name is yafeng, my age is 18! # Take the values passed in by format as a list, and then use to get values >>> str4 = 'my name is , my age is !'.format('yafeng', 18) >>> str4 my name is yafeng, my age is 18! >>> str4 = 'my name is , my age is !'.format('yafeng', 18) >>> str4 my name is 18, my age is yafeng! >>> str4 = 'my name is , my age is !'.format('yafeng', 18) >>> str4 my name is 18, my age is 18! # format parentheses can completely disorganize the order when passing parameters, but they can still pass values for the specified parameters by name. Name = 'yafeng' is passed to >>> str4 = 'my name is , my age is !'.format(age=18,name='yafeng') >>> str4 'my name is yafeng, my age is 18!' >>> str4 = 'my name is , my age is !'.format(name='yafeng', age=18) >>> str4 'my name is yafengyafengyafeng, my age is yafeng!' 5,split,rsplit # Split will split the string from left to right, and you can specify the number of times to cut >>> str5='yafeng:/6/6/6' >>> str5.split('/',1) ['yafeng', '6/6/6'] # rsplit is just the opposite of split. It cuts from right to left. You can specify the number of cuts >>> str5='6|6|8' >>> str5.rsplit('|',1) ['6|6', '8'] 6,join # Take multiple strings from the iteratable object, and then splice them according to the specified separator. The splicing result is string >>> '%'.join('hello') # Take multiple strings from the string 'hello' and splice them with% as the separator 'h%e%l%l%o' >>> '|'.join(['yafeng','18','read']) # Extract multiple strings from the list and splice them with * as a separator 'yafeng|18|read' 7,replace # Replace the old character in the string with a new character >>> str7 = 'my name is yafeng, my age is 18!' # Change the age of yafeng from 18 to 22 >>> str7 = str7.replace('18', '22') # Syntax: replace('old content ',' new content ') >>> str7 my name is yafeng, my age is 22! # You can specify the number of modifications >>> str7 = 'my name is yafeng, my age is 18!' >>> str7 = str7.replace('my', 'MY',1) # Change only one my to my >>> str7 'MY name is yafeng, my age is 18!' 8,isdigit # Judge whether the string is composed of pure numbers, and the return result is True or False >>> str8 = '1314520' >>> str8.isdigit() True >>> str8 = 'yafeng666' >>> str8.isdigit() False
- String knowledge
# 1.find,rfind,index,rindex,count # 1.1 find: find the starting index of the substring from the specified range, return the number 1 if found, and - 1 if not found >>> msg='yafeng say hello' >>> msg.find('f',1,3) # Find the index of character o in characters with index 1 and 2 (regardless of the end) 1 # 1.2 index: the same as find, but an error will be reported if it cannot be found >>> msg.index('n',2,4) # Value error # 1.3 rfind and rindex: omitted # 1.4 count: count the number of times a string appears in a large string >>> msg = "hello everyone" >>> msg.count('e') # Count the number of occurrences of string e 4 >>> msg.count('e',1,6) # Number of occurrences of string e in index 1-5 range 1 # 2.center,ljust,rjust,zfill >>> name='yafeng' >>> name.center(30,'-') # The total width is 30, the string is displayed in the middle, not enough - fill -------------yafeng------------- >>> name.ljust(30,'*') # The total width is 30, the string is aligned to the left, not filled with * yafeng************************** >>> name.rjust(30,'*') # The total width is 30, the string is aligned to the right, not filled with * **************************yafeng >>> name.zfill(50) # The total width is 50, the string is right aligned, not enough to be filled with 0 00000000000000000000000000000000000000000000yafeng # 3.expandtabs >>> name = 'yafeng\thello' # \t for tab >>> name yafeng hello >>> name.expandtabs(1) # Modify \ tnumber of spaces represented by tabs yafeng hello # 4.captalize,swapcase,title # 4.1 capitalization >>> message = 'hello everyone nice to meet you!' >>> message.capitalize() Hello everyone nice to meet you! # 4.2 swapcase: case flip >>> message1 = 'Hi girl, I want make friends with you!' >>> message1.swapcase() hI GIRL, i WANT MAKE FRIENDS WITH YOU! #4.3 title: capitalize each word >>> msg = 'dear my friend i miss you very much' >>> msg.title() Dear My Friend I Miss You Very Much # 5.is digital series #In Python 3 num1 = b'4' #bytes num2 = u'4' #unicode is unicode without u in python3 num3 = 'Four' #Chinese numerals num4 = 'Ⅳ' #Rome digital #isdigt:bytes,unicode >>> num1.isdigit() True >>> num2.isdigit() True >>> num3.isdigit() False >>> num4.isdigit() False #Isdecimal: Unicode (no isdecimal method for bytes type) >>> num2.isdecimal() True >>> num3.isdecimal() False >>> num4.isdecimal() False #IsNumeric: Unicode, Chinese number, Roman number (no IsNumeric method for bytes type) >>> num2.isnumeric() True >>> num3.isnumeric() True >>> num4.isnumeric() True # Three cannot judge floating point >>> num5 = '4.3' >>> num5.isdigit() False >>> num5.isdecimal() False >>> num5.isnumeric() False ''' //Conclusion: //The most commonly used is isdigit, which can judge the types of bytes and unicode, which is also the most common digital application scenario //If you want to judge Chinese numbers or roman numbers, you need to use isnumeric. ''' # 6.is other >>> name = 'yafeng123' >>> name.isalnum() #Strings can contain either numbers or letters True >>> name.isalpha() #String contains only letters False >>> name.isidentifier() True >>> name.islower() # Whether the string is pure lowercase True >>> name.isupper() # Whether the string is pure uppercase False >>> name.isspace() # Whether the string is full of spaces False >>> name.istitle() # Whether the initial letters of words in the string are all uppercase False
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list
Definition: separate multiple values of any data type with commas within []
l1 = [1,'a',[1,2]] (essence: l1 = list([1,'a',[1,2]])
List priority knowledge
# 1. Value by index memory (forward access + reverse access): can be saved or retrieved # 1.1 forward direction (from left to right) >>> my_friends=['yafeng','jason','tom',4,5] >>> my_friends[0] yafeng # 1.2 reverse access (negative sign means right to left) >>> my_friends[-1] 5 # 1.3 for list, the value of specified location can be modified according to index or index. However, if index does not exist, an error will be reported >>> my_friends = ['yafeng','jack','jason',4,5] >>> my_friends[1] = 'martthow' >>> my_friends ['yafeng', 'martthow', 'jason', 4, 5] # 2. Slice (look at the head and ignore the tail, step size) # 2.1 take care of the head and ignore the tail: take out the elements with an index of 0 to 3 >>> my_friends[0:4] ['yafeng', 'jason', 'tom', 4] # 2.2 step size: 0:4:2. The third parameter 2 represents step size. It will start from 0 and accumulate one 2 at a time, so the elements of index 0 and 2 will be taken out >>> my_friends[0:4:2] ['yafeng', 'tom'] # 3. length >>> len(my_friends) 5 # 4. Member operations in and not in >>> 'yafeng' in my_friends True >>> 'xxx' not in my_friends True # 5. add # 5.1 append() append elements at the end of the list >>> l1 = ['a','b','c'] >>> l1.append('d') >>> l1 ['a', 'b', 'c', 'd'] # 5.2 extend() adds multiple elements at the end of the list at one time >>> l1.extend(['a','b','c']) >>> l1 ['a', 'b', 'c', 'd', 'a', 'b', 'c'] # 5.3 insert() inserts an element at a specified location >>> l1.insert(0,"first") # 0 indicates interpolation by index position >>> l1 ['first', 'a', 'b', 'c', 'alisa', 'a', 'b', 'c'] # 6. delete # 6.1 del >>> l = [11,22,33,44] >>> del l[2] # Delete element with index 2 >>> l [11,22,44] # 6.2 pop() deletes the last element of the list by default and returns the deleted value. You can specify the deleted element by adding index value in parentheses >>> l = [11,22,33,22,44] >>> res=l.pop() >>> res 44 >>> res=l.pop(1) >>> res 22 # 6.3 remove() indicates which element to delete with the name in parentheses. There is no return value >>> l = [11,22,33,22,44] >>> res=l.remove(22) # Find the element to be deleted in the first bracket from left to right >>> print(res) None