brief introduction
Python is a very simple language.
Python is an interpretive language that uses indentation alignment to organize code execution.
1, 6 standard data types:
Number String List Tuple Sets Dictionary
Where,
Number String Tuple Sets is immutable data
List Dictionart is variable data
2. Basic grammar:
Operator:
| Comparison operator | <,<=,>,>=,==,!= |
| Escape Character | \n Wrap \Quote \Backslash |
| Arithmetic Operators | +, -, *, / (division of floating point numbers), //(division of integers), ** (power) |
| Logical operators | and,or,not |
| Assignment Operators | = |
| Identity Operator | is, is not,in ,not in |
Python comparison operators can be used concurrently without self-increasing or self-decreasing
Bit and Arithmetic > Comparison > Copy
3. Select Structure
| Single branch structure: | if conditional statement: #Conditional statement cannot be assigned but can== print(" ") |
| Double branch structure: | if. conditional statement else Conditional Statement |
| Ternary conditional operator: | if (conditional expression) else value when the condition is true |
| Multi-branch structure: | if. conditional statement elif. Conditional statement |
4. Cycle structure
The while loop structure:
a = 1
sum=0
while a<=100:
sum = sum + a
a =a+1
print(sum)The difference between break and continue:
break closes the entire loop
continue ends this cycle
5. zip() Parallel List
Method of parallel list operation
names = ("jiaqi","ziyu","jiayu")
ages = (16,17,18)
jobs = ("programmer","art","player")
for name,age,job in zip(names,ages,jobs):
print("{0}--{1}--{2}".format(name,age,job))
for i in range(3):
print("{0}--{1}--{2}".format(names[i],ages[i],jobs[i]))
6. Generator
Generator can only be called once, and the second call is empty
a = (x for x in range(4)) print(a) <generator object <genexpr> at 0x000001A12C2004A0>
a = (x for x in range(4)) print(tuple(a)) print(tuple(a)) (0, 1, 2, 3) 0
7. String slice operation
(Start offset: End offset: Step)
(Start offset: end offset) Header does not end
Steps are -1 reverse extraction from right to left
8. Form function
a = "The name is:{0},Age is:{1}"
b = a.format("Fat and fat",18)
b #Output b
'The name is: Fat and fat,Age: 18'9. Fill and align
^ < > Center aligned left aligned right aligned, followed by bandwidth
: Character followed by a fill, can only be a character, if not specified, the default is space
>>>"{:*>8}".format("245")
'*****245'
>>>"I am{0},My favorite number is{1:*^8}".format(Fat, 666)
'I'm fat, and my favorite number is**666***'10. Sequence
range() can help us easily create a list of integers in the syntax:
range[[start] end [step]]
start optional otherwise defaults to 0
End is required to represent the end number
Step is optional for step
list(range(20,30,4)) [20, 24, 28]
Increase of list elements:
append()
a = [20,40] a.append(80) a [20,40,80]
+
a = [20,40] a = a +[50] [20,40,50]
extend()
a = [20,40] a.extend([50,60]) [20,40,50,60]
insert() anywhere
a = [10,20,30] a.insert(2,100) a [10,20,100,30]
Multiplication extension
[10,20]*3 [10,20,10,20,10,20]
List element deletion:
del
A = [100,200,300,400] del A[2] A = [100,200,400]
pop() deletes the element at the specified location, or the last element in the list if not specified
a = [10,20,30,40,50] a.pop() a = [10,20,30,40] a.pop(1) a = [10,30,40]
remove() deletes the first occurrence of an element
a = [10,20,30,40,50] a.remove[20] a = [10,30,40,50]
Access and Counting of List Elements
index()
a = [10,20,30,40,50,20,30,20,30] a.index(20) 1 a.index(20,3) The first 20 after the index position 5
count() Gets the number of occurrences of a character
len() Returns the length of the list
a = [10,20,30] len(a) 3
11. Tuple creation
a= 1,2,3) or a= 1,2,3
There is only one time a=(1,)
12. Dictionaries
1) Definition:
a ={'name':'jiaqi','age':18,'job':'programmer'}
a = dict(name='jiaqi',age=18,job='programmer')
a = dict([("name","jiaqi"),("age",18)])2) Access to dictionary elements:
a={'name':'jiaqi','age':18,'job':'programmer'}a['name'] 'jiaqi'
get()
a.get('name') a.get('name','ddd')Not Occasionally'ddd'a.items() #List all key-value pairs
dict_items([('name', 'jiaqi'), ('age', 18), ('job', 'programmer')])a.keys()
dict_items([('name', 'jiaqi'), ('age', 18), ('job', 'programmer')])len(a) 3
"name"in a True
3) Addition, modification and deletion of dictionary elements:
update() adds all key values from the new dictionary to the old dictionary object, overwriting them directly if they are repeated
b={'name':'jiaqi','money':1000','sex':'nv'}
a.update(b)
a {'name':'jiaqi','age':17,'job':'programmer','money':1000,'sex':'nv'}del() Delete the specified key
pop
b=a.pop('age') b 17 Delete and assign a value to b
clear () Delete all keys
4) Sequence unpacking:
Assigning values to multiple variables
s={'name':'jiaqi','age':18,'job':'programmer'}
name,age,job=s #Default key operations
name
'name'
name,age,job=s.items() #Operations on key values
name
{'name','jiaqi'}
name,age,job=s.values() #Operating on values
name
'jiaqi'
13. Tabular data use and list storage
r1={"name":"Less One","age":18,"salary":30000,"city":"Beijing"}
r2={"name":"Waiter","age":17,"salary":40000,"city":"Shanghai"}
r3={"name":"Junior Three","age":16,"salary":60000,"city":"Shenzhen"}
tb = [r1,r2,r3]
#Get second-line pay
print(tb[1].get("salary"))
#Pay for everyone in the printed form
for i in range(len(tb)):
print(tb[i].get("salary"))
#Print all data in the table
for i in range(len(tb)):
print(tb[i].get("name"),tb[i].get("age"),tb[i].get("salary"),tb[i].get("city"))14. Sets
add() Add () is not repeatable
a = {3,4,7}
a.add(9)set() Converts an iterative object, such as a list tuple, into a set, leaving only one if there is duplicate data in the original data
a = {'a','b','c','b'}
b = set(a)
b = {'a','b','c'}remove() deletes the specified element, clear() empties the entire collection
a = {10,20,30,40,50}
a.remove(20)
a = {10,30,40,50}Collection related operations
a={1,3,'s'}
b={'he','s','gt'}
a|b #union
{1,3,'s','he','gt'}
A&b #Intersection
{'s'}
a-b #difference set
{1,3}
a.union(b) #union
a.intersection(b) #intersection
a.difference(b) #difference set
15. Other Knowledge Points
strip() removes the specified information at the beginning and end of a string
" sfhjdf ". strip() output "sfhjdf"
lstrip() Removes the information to the left of the string
rstrip() removes the information to the right of the string
a="YUJIAQI love to play program very much"
a.capitalize() produces a new string with the first letter capitalized
a.title() produces a new string The first letter of each word is capitalized
a.upper() All characters are capitalized
a.lower() All characters are lowercase
a.swapcase() All letter case conversions
Is isalnuml() a letter or a number
isalpha() checks whether a string is composed of only letters (or Chinese characters)
isdigital() checks whether a string consists of numbers
isspace() checks for whitespace
Is isupper() a capital letter
Is islower() a lowercase letter