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Digital Number

Integer (int)-often referred to as an integer or integer, is a positive or negative integer without a decimal point. Python3 integers are unlimited in size and can be used as Long types. Bool is a subtype of integers.

Floating point type (float)-A floating point type consists of an integer part and a fractional part, and can also be represented by scientific counting (2.5e2 = 2.5x 102250)

The complex number ((complex))-the complex number consists of the real part and the imaginary part, which can be denoted by a + bj or complex (aline b). Both the real part an and the imaginary part b of the complex number are of floating point type.

Digital type conversion

Int (x) converts x to an integer.

Float (x) converts x to a floating point number.

Complex (x) converts x to a complex number, where the real part is x and the imaginary part is 0.

Complex (x, y) converts x and y to a complex number, where the real part is x and the imaginary part is y. X and y are numeric expressions.

Numeric operation # +-* /% (remainder) * * (exponentiation) # in integer division, division / always returns a floating point number. # if you only want to get the result of an integer and discard possible fractions, you can use the operator / / print (8 / 5) # 1.6print (8 / / 5) # Note: / / you don't necessarily get a number of integer type. It is related to the data type of the denominator print (8 / / 5. 0) # 1. Query the square 25 string str string of the exponentiation print (5 * 2) # 5 using the * * operation

Index (): finds the location where the substring substr appears for the first time, and throws a ValueErrorrindex () exception if the substring does not exist

Rindex (): finds the location of the last occurrence of the substring substr, and throws a ValueError () exception if the substring does not exist

Find (): finds the location where the substring substr appears for the first time, and returns-1 if the substring does not exist

Rfind (): finds the location of the last occurrence of the substring substr, and returns-1 if the substring does not exist

S = 'hello, hello'print (s.index (' lo')) # 3print (s.find ('lo')) # 3print (s.find (' k')) #-1print (s.rindex ('lo')) # 10print (s.rfind (' lo')) # 10 string case conversion

Upper (): converts all characters in a string to uppercase letters

Lower (): converts all characters in a string to lowercase letters

Swapcase (): converts all uppercase letters in a string to lowercase letters and all lowercase letters to uppercase letters

Capitalize (): converts the first character to uppercase and the rest to lowercase

Title (): converts the first character of each word to uppercase and the remaining characters of each word to lowercase

S = 'hello, Python'print (s.upper ()) # HELLO, PYTHONprint (s.lower ()) # hello, pythonprint (s.swapcase ()) # HELLO, pYTHONprint (s.capitalize ()) # Hello, pythonprint (s.title ()) # Hello, Python string alignment

Center (): Center alignment. The first parameter specifies the width, and the second parameter specifies the filler. The default is space. If the set width is less than the actual width, the original string is returned.

Ljust (): left alignment, the first parameter specifies the width, the second parameter specifies the filler, the default is a space, and if the set width is less than the actual width, the original string is returned

Rjust (): right-aligned, the first parameter specifies the width, the second parameter specifies the filler, the default is a space, and the original string is returned if the set width is less than the actual width

Zfill (): align to the right and fill the left with 0. This method takes only one parameter to specify the width of the string. If the specified width is less than or equal to the length of the string, the string itself is returned.

S = 'hello,Python'''' Center alignment' print (s.center (20,'*')) # * hello,Python****''' left alignment''print (s.ljust (20,' *')) # hello,Python*print (s.ljust (5,'*)) # hello,Python''' right alignment''print (s.rjust (20) ('*')) # * hello,Python''' right align, fill with 0''print (s.zfill (20)) # 000000hellodPythonprint ('-1005'.zfill (8)) #-0001005 string splitting, slicing

Split

Split (): split from the left side of the string

Rsplit (): splits from the right side of the string

The default split character is a space, and the return value is a list

Specify the splitter of the split string through the parameter sep

Specify the maximum number of times to split the parity string through the parameter maxsplit. After the maximum number of splits, the remaining substrings will be taken as a separate part.

S = 'hello word Python'print (s.split ()) # [' hello', 'word',' Python'] S1 = 'hello | word | Python'print (s1.split (sep=' |')) # ['hello',' word', 'Python'] print (s1.split (' | |, 1)) # ['hello',' word | Python'] # start print (s1.rsplit ('| |, 1)) # ['hello | word' 'Python'] # start on the right

Slice

S = 'hello,world'print (s [: 5]) # hello starts at index 0 and ends at 4 print (s [6:]) # world starts at index 6 and goes to the last element print (s [1: 5:1]) # ello starts at index 1 and ends at 4 with a step of 1print (s [:: 2]) # hlowrd from start to end and a step of 2print (s [:-1]) # dlrow,olleh Starting from the last element (index-1), to the end of the first element print (s [- 6 1]) #, world starts from index-6 to the last end string to determine the correlation

Isidentifier (): determines whether the specified string is a legal identifier

Isspace (): determines whether the specified string consists entirely of white space characters (carriage return, line feed, horizontal tab)

Isalpha (): determines whether the specified string is composed entirely of letters

Isdecimal (): determines whether the specified string consists entirely of decimal numbers

Isnumeric (): determines whether the specified string is composed entirely of numbers

Isalnum (): determines whether the specified string consists entirely of letters and numbers

String other operations

String substitution

Replace ()

S = 'hello,Python,Python,Python'print (s.replace (' Python', 'Java')) # replace all hello,Java,Java,Javaprint by default (s.replace (' Python', 'Java', 2)) # set the number of replacements hello,Java,Java,Python

String concatenation

Join ()

Lst = ['hello',' java', 'Python'] print (', '.join (lst)) # hello,java,Pythonprint (' | '.join (lst)) # hello | java | output of Python format string

% placeholder: add% before output, multiple parameters with parentheses and commas

% s string

Integer% I or% d

-% f floating point number

{} placeholder: call the format () method

F-string: write variables in {}

Name = 'Zhang San' age = 20print ('my name is% s, this year% d year'% (name, age)) print ('my name is {0}, this year {1} year, nickname is also {0} (name, age)) print (f'my name is {name}, this year {age} year') # my name is Zhang San, I am 20 years old this year, my nickname is Zhang San # my name is Zhang San, I am 20 years old this year

Set the width and precision of the number

# set width and precision of digits''% occupancy 'print (' d'% 99) # 10 indicates width print ('.3f'% 3.1415926) # .3f represents 3 decimal places print ('.3f'% 3.1415926) # both width and precision''{} placeholder need to be used: start''print (' {: .3} '.format (3.1415926) ) # .3 represents 3 significant digits print ('{: .3f} '.format (3.1415926)) # .3f represents the last 3 decimal places print (' {: 10.3f} '.format (3.1415926)) # .3f represents the last 3 decimal places # 99' 3.14 '3.142' 3.14 '3.14' 3.142 string encoding s = 'long-lasting' # Encoding converts a string to byte (binary) data print (s.encode (encoding='gbk')) # gbk Chinese occupies 2 bytes print (s.encode (encoding='utf-8')) # utf-8, Chinese occupies 3 bytes # decoding converts byte (binary) into string data # encoding and decoding The encoding method requires consistent byte = s.encode (encoding='gbk') print (byte.decode (encoding='gbk')) # b'\ xb5\ xab\ xd4\ xb8\ xc8\ xcb\ xb3\ xa4\ xbe\ xc3'# b'\ xe4\ xbd\ x86\ x84\ xbf\ xe4\ xba\ xba\ xe9\ x95\ xbf\ xe4\ xb9\ x85 wish the characteristics of the list list

Ordered sequence

Index mapping only one data

Duplicate data can be stored

Mixed storage of any data type

Dynamically allocate and reclaim memory as needed

Creation of list

[]: use square brackets

List (): use the built-in function list ()

List generation

Syntax format: [iTuni for i in range (I, 10)]

Explanation: I represents a custom variable, I represents an expression of a list element, and range (I, 10) represents an iterable object

Print ([I * i for i in range (1,10)]) # [1, 4, 9, 16, 25, 36, 49, 64, 81] list element query

Determine whether the specified element exists in the list

In / not in

Traversal of list elements

For item in list: print (item)

Query element index

List.index (item)

Get element

List = [1, 4, 9, 16, 25, 36, 49, 64, 81] print (list [3]) # 16print (list [3:6]) # [16, 25, 36] addition of list elements

Append (): add an element to the end of the list

Extend (): add at least one element to the end of the list

Insert0: adds an element at the specified location in the list

Slicing: adding at least one element at a specified location in the list

Deletion of list elements

Rerove (): delete one element at a time

Duplicate element deletes only the first one

There is no ValceError exception thrown in the element

Pop (): deletes an element at a specified index location

No IndexError exception is thrown in the specified index

Delete the last element in the list without specifying an index

Slicing: delete at least one element at a time

Clear0: clear the list

Del: delete list

Sorting of list elements

Sort (), all elements in the list are sorted in the order from smallest to largest by default. You can specify reverse= True to sort in descending order, which is an operation on the original list.

List.sort ()

Sorted (), you can specify reverse-True to sort in descending order, so that the original list does not change and a new list is generated.

Summary of sorted (list) knowledge points

The characteristics of tuple tuples.

Tuples in Python are similar to lists, except that the elements of tuples cannot be modified.

Tuples use parentheses and lists use square brackets

Creation of tuples

Use parentheses () directly. Parentheses can be omitted

T = ('Python',' hello', 90)

Using the built-in function tuple (), if there are multiple elements, you must add parentheses

Tuple (('Python',' hello', 90))

A tuple that contains only one element, using parentheses and commas

T = (10,) summary of knowledge points

The characteristics of the dictionary dict

Stored as key-value pairs, key is unique

Key must be an immutable object

Dictionaries are variable sequences

Dictionaries are unordered sequences (Note: since the Python3.7 version, the insertion order retention nature of dict objects has been declared as an official part of the Python language specification. That is, after Python3.7, the dictionary is an ordered sequence, and the order is the insertion order of the dictionary)

The creation of a dictionary

{}: use curly braces

Use the built-in function dict ()

Zip (): dictionary generator

Items = ['fruits',' Books', 'Others'] prices = [12, 36, 44] d = {item.upper (): price for item, price in zip (items, prices)} print (d) # {' FRUITS': 12, 'BOOKS': 36,' OTHERS': 44} dictionary element acquisition

[]: [] value

Scores [Zhang San]. If key does not exist, throw a keyError exception

The get (): get () method takes a value. If key does not exist, None is returned. You can also set the default return value.

New dictionary element user = {"id": 1, "name": "zhangsan"} user ["age"] = 25print (user) # {'id': 1,' name': 'zhangsan',' age': 25} dictionary element modification user = {"id": 1, "name": "zhangsan", "age": 25} user ["age"] = 18print (user) # {'id': 1,' name': zhangsan'' Deletion of 'age': 18} dictionary elements

Del: delete a specified key-value pair or delete a dictionary

User = {"id": 1, "name": "zhangsan"} del user ["id"] print (user) # {'name':' zhangsan'} del user

Claer (): clear the elements in the dictionary

User = {"id": 1, "name": "zhangsan"} user.clear () print (user) # {} get dictionary view

Keys (): gets all the key in the dictionary

Values (): gets all the value in the dictionary

Items (): gets all key,value key-value pairs in the dictionary

Traversal of dictionary elements

Traverse key, and then get value through key

Scores = {'Zhang San': 100,'Li Si': 95, 'Wang Wu': 88} for name in scores: print (name, scores [name])

Traversing key,value at the same time through the items () method

Scores = {'Zhang San': 100,' Li Si': 95, 'Wang Wu': 88} for name, score in scores.items (): summary of knowledge points of print (name, score)

The characteristics of set sets

The set is a variable sequence.

Collections are dictionaries without value

Elements in the collection do not repeat

The elements in the collection are unordered

Creation of a collection

{}

S = {'Python',' hello', 90}

Built-in function set ()

Print (set ("Python")) print (set (range (1pr 6)) print (set ([3,4,7]) print (set ((3,2,0)) print (set ({"a", "b", "c"})) # defines an empty set: set () print (set ())

Set generation

Print ({I * i for i in range (1,10)}) # {64, 1, 4, 36, 9, 16, 49, 81, 25} set operation

Judgment operation of set elements

In / not in

New operations for collection elements

Add (): add one element at a time

Update (:) adds multiple elements

Delete operation of collection element

Remove (): deletes a specified element and throws a KeyError if the specified element does not exist

Discard (:) deletes a specified element and does not throw an exception if the specified element does not exist

Pop (): randomly delete an element

Clear (): clear the collection

The relationship between sets

Whether two sets are equal: you can use the operator = = or! = to determine whether the elements are equal as long as the elements are the same

Whether one set is a subset of another: issubset ()

S1 = {10,20,30,40,50,60} S2 = {10,30,40} S3 = {10,70} print (s2.issubset (S1)) # Trueprint (s3.issubset (S1)) # False

Whether one set is a superset of another: issuperset ()

Print (s1.issuperset (S2)) # Trueprint (s1.issuperset (S3)) # False

Whether the two sets do not intersect: isdisjoint ()

S1 = {10,20,30,40,50,60} S2 = {10,30,40} s3 = {20,70} print (s1.isdisjoint (S2)) # False with intersection print (s3.isdisjoint (S2)) # True mathematical operation without intersection set

Intersection: intersection () and & equivalence, the intersection of two sets

S1 = {10,20,30,40} S2 = {20,30,40,50,60} print (s1.intersection (S2)) # {40,20,30} print (S1 & S2) # {40,20,30}

Union: union () and | equivalent, the union of two sets

Print (s1.union (S2)) # {40,10,50,20,60,30} print (S1 | S2) # {40,10,50,20,60,30}

Difference sets: difference () and-equivalent

Print (s2.difference (S1)) # {50,60} print (S2-S1) # {50,60}

Symmetric difference: symmetric_difference () is equivalent to ^

Print (s2.symmetric_difference (S1)) # {10,50,60} print (S2 ^ S1) # {10,50,60} knowledge points summary

List, tuple, dictionary, collection summary

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