1.Python
1. Data Type
1. Numbers
 Integer : int
 float: float
 Plural: complex
 boolean: bool
2. String
 String: String
3. Differences from Java

python has only four kinds of data: integers, longs, floats, and complexes

java has char, short,byte, int, long, float,double types
4. List

A list is an ordered sequence of python objects

list creation
list1 = [1,2.0,'hello']

list of values
##Take the above list as an example list1[0] ##output: 1 list1[list1.len()1] ##Output result: hello

list slice
list2 = [1,2.0,3,4,5,6] list2[2,1] ##Output result: [3,4,5]

delete list element
##Take the above list as an example del list2[0] ##Output result: [2.0,3,4,5,6]

Common method
## 1. Delete del list2[0] ## 2. Return the number of occurrences of an element in the list list2.count(1) ## 3. Returns the first position where the element appears list2.index('hello') ## 4. Append the element at the end of the list list2.append('world') ## 5. Delete the element at the specified position in the list list2.pop(0) ## 6. Sort the list list2.sort()
5. Tuples

The characteristics of tuples are: once created, they cannot be changed

tuple creation
## 1. Create a tuple with a pair of parentheses t = (1,2,3,4,5) ## 2. The number of tuples exceeds two parentheses can be omitted t = 1,2,3,4,5 ## 3. Note that when the number of elements in the tuple is only one parenthesis cannot be omitted t = (1)

tuple of values
##Take the above t as an example t[0] ##output: 1

tuple slice
##Take the above t as an example t[1:3] ##Output result: (3,4)

Due to the immutability of tuples, there are no methods like insert
6. Dictionary

A dictionary is a data structure consisting of "keyvalue"

Note: When the dictionary gets the key, it is not repeatable. If it is repeated, it will be overwritten by the last one, so there will be no repetition. At the same time, the dictionary is unordered.

dictionary creation
## 1. Create an empty dictionary a = {} ## 2. Direct assignment b = {'one':1,'two':2}

Insert an element into a dictionary by index
##Take a above as an example a['one'] = 1 ##Result: a changes from the original empty dictionary to a dictionary with one element: {'one':1}

You can also use the above method to assign

Common method
##Take b above as an example ## 1.key() method b.key() ##Output result: ['one','two'] ## 2.value() method b.value() ##Output result: [1,2]
2. Cycle
1.for loop

Fixed number of cycles

for i in range(5) : print(i) ##output 0 1 2 3 4

traverse

languages = ["C", "C++", "Perl", "Python"] for x in languages: print (x) """ result C C++ Perl Python >>> """
2.while loop

n = 100 sum = 0 counter = 1 while counter <= n: sum = sum + counter counter += 1 print("1 arrive %d The sum is: %d" % (n,sum)) ##Result: The sum of 1 to 100 is: 5050
3. Positive triangle, inverted triangle source code

right

#The format in the upper right corner outputs the ninetynine multiplication table for i in rang(1,10): for k in rang(1,i): print(end = " ") for j in rang(i,10): print("%d*%d = %2d" % (i,j,i*j),end=" ") print(" ") #The lower right triangle format outputs the ninetynine multiplication table for i in rang(1,10): for k in rang(1,10i): print(end = " ") for j in rang(1,10i): print("%d*%d = %2d" % (i,j,i*j),end=" ") print(" ")

left

#The number of the lower left triangle outputs the ninenine multiplication table for i in rang(1,10): for j in rang(1,i+1): print("%d*%d = %2d" % (i,j,i*j),end=" ") print(" ") #The upper left triangle format outputs the ninetynine multiplication table for i in rang(1,10): for j in rang(1,i+1): print("%d*%d = %2d" % (i,j,i*j),end=" ") print(" ")
4. Pay attention
 python syntax
 Strictly indent
 The loop is followed by a colon
2.Pandas
1. Basic Concepts

Series

Series: Series, also known as a sequence, is used to store a row or column of data, as well as an index collection associated with it
Series([data 1,data 2,...],index = [index 1,Index 2,...])

Note the following points
 Series is a onedimensional arraylike object
 His data structure has no restrictions
 He has an index, similar to a dictionary
 Series functions as both numbers and dictionaries


DataFrame

DataFrame is a collection of data that stores multirow and multicolumn data, and is a container for Series
from pandas import Series from pandas import DataFrame df = DataFrame({'age':Series([26,29,24]),'name':Series(['Ken','Jerry','Ben'])},index=[1,2,3])

2. Group analysis

Grouping analysis: refers to a method of dividing the analysis object into different parts according to the grouping field to compare and analyze the differences between the groups

Commonly used methods are count, sum, average

common form
df.groupby(by = ['Category 1','Category 2',...])['Columns to be counted'].agg({Column Alias 1: Statistical Function 1, Column Alias 2: Statistical Function 2})
df.groupby(by=[u'class'，u'gender'])[u'military training'].agg((u'total score':numpy.sum,u'number of people':numpy.sizey,u'average value':nmpy.mean,u'variance':numpy.var,u'standard deviation':numpy.std,u'highest score':umpy.max,u'Lowest score':numpy，min))
result:
3. Data visualization

Scatter chart: A scatter chart is a graph that uses one variable as the abscissa and another variable as the ordinate, and uses the distribution pattern of scatter points (coordinate points) to reflect the relationship between variables. The relevant methods are as follows:
plt.plot(x,y,'.',color=(r,g,b) plt.xlabel('x axis coordinates') plt.ylabel('y axis coordinates') plt.grid(True) #Among them, x and y are the sequence of the xaxis and the yaxis: '.' ('o', etc.) represents the small point (large point, etc.); color is the color of the scatter plot, which can be defined by RGB or English letters Defines how RGB colors are set as (red, green, blue)

Line chart: P134
3. Bayesian
slightly