## Beginners can understand the introduction of python at a glance

First introduce the most basic usage of math. Using math can help you better perform simple calculations, such as square, root, etc.

import math math.sqrt(12.0) dir(math)

dir() returns all properties and methods of the specified object without values.

This function will return all properties and methods, even the default built-in properties of all objects.

from math import cos # import cos into the namespace cos(0.4) # no need to write math.cos from math import * # import all functions sqrt(4.0)

Next, let's explain how to judge whether it belongs to different types

Variables are dynamically typed, that is, they do not need to be explicitly declared

a = 1 type(a) #result is int b = 1.0 type(b) #result is float b = a type(b) #result is int x = True x = False type(x) #result is Bool x = 1.0 + 4.0j type(x) #result is complex

Calculation inevitably uses various operation symbols. The following is a common single operation symbol

20 + 3, 20 - 3 20 * 3, 20 / 3, 20.0 / 3 # Note, *integer* division 20 % 3, 20.5 % 3.1 # Modulus, i.e. remainder a = 1; a +=1 ; print(a) a *= 5; print(a)

4 > 7, 4 < 7, 4 >= 7, 4 <= 7 4 == 7, 4 != 7

Logical operation

4 > 7 and 4 < 7 #result is False 4 > 7 or 4 < 7 #result is True not 4 > 7 #result is True

Compound type: string, list, set, dictionary

character string:

city = "Sheffield" type(city) #result is str city = 'Sheffield' # can use " or ' type(city) #result is str city[0] # strings are like lists characters #result is s 'Jon' + ' ' + 'Barker' # string concatenation #result is 'Jon Barker' city.upper(), city.lower() help(str)

When you are not sure what you should do, use help(str), which will display the help about the class str in the built-in module

For example:

add(self, value, /)

Return self+value.

contains(self, key, /)

Return key in self.

eq(self, value, /)

Return self==value.

format(self, format_spec, /)

Return a formatted version of the string as described by format_spec.

ge(self, value, /)

Return self>=value.

getattribute(self, name, /)

Return getattr(self, name).

getitem(self, key, /)

Return self[key].

A list is similar to a string, but elements can be of any type

List:

primes = [2, 3, 5, 7, 11] type(primes) #result is list weird = [1, 'Monday', 1.4, False, 4+5j] # Mixed types print(weird) #result is [1, 'Monday', 1.4, False, (4+5j)]

Use the data in the list:

days = ['Mon', 'Tues', 'Weds', 'Thur', 'Fri', 'Sat', 'Sun'] days[0] #result is 'Mon' days[1:3] #result is ['Tues', 'Weds'] days[:] #result is ['Mon', 'Tues', 'Weds', 'Thur', 'Fri', 'Sat', 'Sun'] days[3:] #result is ['Thur', 'Fri', 'Sat', 'Sun'] days[::2] #result is ['Mon', 'Weds', 'Fri', 'Sun']

List operations: append, count, extend, index, insert, pop-up, delete, reverse, sort

days = ['Mon', 'Tues', 'Weds', 'Thur', 'Fri', 'Sat', 'Sun'] days.reverse() print(days) days.sort() print(days) #result is ['Fri', 'Mon', 'Sat', 'Sun', 'Thur', 'Tues', 'Weds'] x = [1, 2, 3, 4] x.extend([5, 6, 7]) print(x) x = list('Let us go then, you and I') x.count('e'), x.count(' ')

Sort here adds that it sorts the Mondays to Sundays in the list in alphabetical order. Sort does not have to be like this. You can also define how you want to sort all the information in the list.

tuples are immutable lists, that is, once created, they cannot be modified.

x = (1, 2) type(x) print(x[0]) #result is 1

Parentheses are not absolutely necessary

pos1 = (10, 20, 30) pos2 = (10, 25, 30) pos1 == pos2 #result is False

true if all elements are equal

x, y = 10, 15 x, y = y, x print(x, y) #result is 10,15

You can swap variables with one line

Entries in the collection must be unique. Sets use curly braces.

x = {1, 2, 3, 4, 3, 2, 1, 2} print(x) #result is {1, 2, 3, 4} print({1,2,3,7,8, 9}.intersection({1,3,6,7,10})) print({1,2,3,7,8, 9}.union({1,3,6,7,10})) print({1,2,3,7,8, 9}.difference({1,3,6,7,10})) #result is {1, 3, 7} # {1, 2, 3, 6, 7, 8, 9, 10} # {8, 9, 2}

A dictionary maps from a unique key to a value

office = {'jon': 123, 'jane':146, 'fred':245} type(office) #result is dict office['jon'] #result is 123 office = {'jon': 123, 'jane':146, 'fred':245, 'jon': 354} print(office['jon']) #result is 354

dict is the abbreviation of dictionaries

The latter item overwrites the previous one, so it defaults to the last value in the dictionary.

Application of dictionary

office['jose'] = 282 # add a new key-value pair print(office) office.keys() office.values() 'jose' in office # check if a key exists

keys export the names of all entries in the dictionary;

value exports the values corresponding to all entries in the dictionary

For more information, please see the introduction python2 that beginners can understand at a glance

I hope you can pay more attention to me. I will share more simple and understandable code methods with you