Programming refers to writing instructions for a computer to execute.

The instructions that a computer executes are called code.

Python is an open source programming language invented by Dutch programmer Guido van Rossum.

Python is already one of the most streamlined and easy-to-learn programming languages ​​in the world. Python can be run on all major operating systems and computers, and can be used in everything from building web servers to creating desktop applications.

Python comes with a program called IDLE, which stands for Interactive Development Environment. We will enter Python code in IDLE.

The program IDLE is called an interactive shell. You can type Python code directly into it and the program will print out the results.

Start the IDLE application, click "File" and select "Create New File". A text editor will open.

Code can be written in a text editor and saved for later running.

The difference between text editing and interactive shell

Programming: Writing commands for a computer to execute.

Code: Instructions written by a programmer for a computer to execute.

Low-level programming languages: Programming languages ​​that are closer to writing instructions in binary (0s and 1s) than high-level programming languages ​​(programming languages ​​that sound more like English).

Assembly Language: A difficult programming language to learn.

High-level programming language: A programming language that sounds more like English than a low-level editing language.

The purpose of comments is to explain what the code does.

Comments are only needed when special operations are performed in the code, or when the code is not clear and easy to understand.

We usually distinguish code by the number of lines of code.

In IDLE, you can open the "Edit" menu and select the "Go to Line" button to jump to the specified line of the program.

In an interactive shell, you can only enter one line of code at a time, and you cannot copy and paste multiple lines of code.

Sometimes a piece of code is longer than one line and can be extended to a new line using triple quotes, parentheses, square brackets or curly brackets.

You can also use backslash\ to wrap the code.

Python divides data into different categories, namely data types.

In Python, each data value is called an object.

A constant is a value that never changes.

A variable refers to a value that changes.

Two types of errors in Python: syntax errors and exceptions.

Python divides operators into multiple types, and arithmetic operators are used for simple arithmetic calculations.

Required parameters: When the user calls the function, all required parameters must be passed in, otherwise Python will report an exception error.

Optional parameters: Functions are passed in only when needed and are not required to execute the program. If no optional parameters are passed in, the function will use their default values.

Function name: The keyword def tells the Python operator that a function is being defined.

Parameters: After naming the function, add a pair of parentheses after the name. In the parentheses are the parameters you want the function to accept.

Definition: Add a colon after the parentheses, then wrap and indent 4 spaces. All code after the colon that is indented by 4 spaces is the definition of the function.

Return value: The keyword return specifies the value output when calling the function, which we call the return value of the function.

Syntax: You can call a function using the syntax "[function name]([comma separated arguments])".

len built-in function indicates the length of the returned object, such as the length of a string (number of characters)

str built-in function, str accepts an object as a parameter and returns a new object (string) with data type str

int built-in function, which accepts an object as a parameter and returns an integer object (integer)

The float built-in function accepts an object as a parameter and returns a floating point number object (decimal)

Note:

The input built-in function, mobile phone user information, accepts a string as a parameter and displays it to the user using the program.

Because functions can be reused, using functions can reduce the amount of code.

The functions of the new program are exactly the same as the previous program, but because the functions are encapsulated in a function that can be called at any time as needed, the amount of code is greatly reduced and the readability is improved.

When you define a variable, its scope refers to which parts of the program can read and write to it.

The scope of a variable is determined by where in the program it is defined.

try clause: contains errors that may occur.

except clause: Contains code that is executed only when an error occurs.

Note: Do not use variables defined by try statements in except statements.

Methods are functions that are closely related to a specified data type.

Methods, like functions, execute code and return results.

Different from functions: methods can only be called on objects.

Parameters can be passed to methods.

Concept: A list is a container that stores objects in a fixed order.

Representation method: Lists are represented by square brackets ([ ]).

Create list syntax:

List features

Concept: A tuple is a container that stores ordered objects.

Representation method: Use parentheses to represent the ancestor, and commas must be used to separate the elements in the ancestor.

Create tuple syntax:

Characteristics of tuple:

Tuple Purpose: Tuples are very useful when dealing with values ​​that you know will never change, and you don't want other programs to modify them.

concept: A dictionary is another built-in container for storing objects. They are used to link two objects, key and value. Linking one object to another, also known as mapping, results in a key-value pair. You can add key-value pairs to a dictionary, and then query the dictionary using the key to obtain its corresponding value. But cannot query using value.

Representation method: Dictionaries are represented by curly brackets ( { } ).

Syntax for creating a dictionary:

Dictionary features:

Example of a program using a dictionary:

Containers can be stored within containers.

Method: A function closely related to the specified data type.

List: A container that stores ordered objects.

Iterable: An object is iterable if every element in the object can be accessed using a loop.

Iterable objects: Iterable objects such as strings, lists, and elements.

Index: A number that represents the position of an element in an iterable object.

Mutable: The contents of the container can change.

Immutable: The contents of the container cannot be changed.

Dictionary: A built-in container for storing objects, mapping an object called a key to an object called a value.

Key: used to find the corresponding value in the dictionary.

value: The value in the dictionary mapped to the key.

Mapping: Linking one object to another.

Key-value pairs: Keys map to values ​​in a dictionary.

If the string spans more than one line, triple quotes can be used.

If you use single or double quotes to define a string that spans multiple lines, Python will report a syntax error.

Like lists and tuples, strings are iterable.

The first character in the string is at index 0, and each subsequent index is incremented by 1.

Python also supports the use of negative indexes to find elements in lists: the search year that can be used to find elements in an iterable object from right to left (must be a negative number).

Strings, like tuples, are immutable and the characters in the string cannot be modified.

If you want to modify it, you must create a new string:

You can use the addition operator to combine two or more strings together. The result is a new string composed of the characters in the first string plus the characters in the other strings.

You can use the multiplication operator to multiply strings and numbers.

You can use the upper method of a string to change each character in the string to uppercase.

You can use the lower method of a string to change each character in the string to lowercase.

You can use the capitalize method of a string to change the first letter of the string to uppercase.

You can use the format method to create a new string, which will replace the "{ }" in the string with the passed-in string.

You can also use the format method to pass variables as parameters:

Curly braces ({ }) can be used repeatedly:

The format method is useful if you want to create a string based on user input:

The split method can be used to split a string into two or more strings.

You need to pass in a string as the parameter of the split method and use it to split the original string into multiple strings.

The split result is a list containing two elements: a string consisting of all characters before the period, and a string consisting of all characters after the period.

The join method adds new characters between each character of the string.

The join method can be called on an empty string or a string containing whitespace characters, passing in a list of strings as arguments, thereby concatenating these strings into a single string.

Use the strip method to remove whitespace characters at the beginning and end of a string.

replace method, the first parameter is the string to be replaced, and the second parameter is the string used to replace. You can use the second string to replace all the same content in the original string as the first string.

You can use the index method to get the index of the first occurrence of a string in a string.

Pass in the character you want to find as a parameter, and the index method can return the index of the first occurrence in the string:

If you are not sure whether there is a matching result, you can use the following exception handling method:

The keyword in can check whether a string is in another string, and the return result is True or False:

Add the keyword not in front of in to check whether a string is not in another string.

String escaping (escaping) refers to adding a symbol before a character with special meaning in Python to tell Python that the symbol represents a character in this case and has no special meaning.

Escape with backslash in Python.

Add to the string to indicate a newline:

Slicing creates a new iterable object from a subset of elements in an iterable object.

Syntax: [Iterable object] [[Start index: End index]]

Note: 1. A slice includes elements at the starting index position, but does not include elements at the ending index position; 2. If the starting index is 0, then the starting index position can be left blank; 3. If the end index is the index of the last element in the iterable object, you can leave the position of the end index blank; 4. If both the starting index and the ending index are left blank, the original iterable object will be returned.

Syntax: "for [variable name] in [iterable object name]: [instruction]"

Function:

range function: and built-in function that creates a sequence of integers.

grammar:

Example (use the range function to create a sequence of numbers and iterate over it): for i in range(1,11): print(i) >>1 ... >>9 >>10

while loop: It is a loop that executes code as long as the expression evaluates to True.

Syntax: "while [expression]: [execute code]"

Infinite loop: If the expression of a defined while loop always evaluates to True, the loop will not stop executing. A loop that never stops executing is also called an infinite loop.

break statement: can be used to terminate the loop.

Whenever Python encounters a break statement, the loop terminates.

continue statement: You can use the statement with the keyword continue to terminate the current iteration of the loop and proceed to the next iteration.

Nested Loops: Loops can be combined in many ways.

Example: #Use two for loops to add all the numbers in one list to all the numbers in the other list list1 = [1,2,3,4] list2 = [5,6,7,8] added = [ ] for i in list1: for j in list2: added.append(i j) print(added) >>[6, 7, 8, 9, 7, 8, 9, 10, 8, 9, 10, 11, 9, 10, 11, 12]

Loop: A section of code that continues to execute until a condition defined in the code is met.

Traversal: Use a loop to access each element in an iterable object.

for loop: A loop used to iterate over iterable objects such as strings, lists, tuples, or dictionaries.

Index variable: The value of the variable is a number that represents the index in the iterable object.

while loop: A loop that continues to execute as long as the value of the expression is True.

Infinite Loop: A loop that never ends.

break statement: A statement with the break keyword, used to terminate the loop.

continue statement: A statement with the keyword continue, used to terminate the current iteration of the loop and enter the next iteration.

Outer loop: A loop that contains nested loops inside.

Inner loop: A loop nested within another loop.

In order to facilitate reading and checking the program, large programs are divided into multiple files containing Python code, called modules.

Import: Before using a module, you need to import the module first, which means writing code to let Python know where to get the module.

Import syntax: import[module name].

After importing a module, you can use its variables and functions.

Built-in module: It comes with the Python language and contains many important functions.

Create module

Import (import) Same as above

Module: Another name for a Python file containing code.

Built-in modules: modules that come with the Python language, including many important functions.

Import: Write code that tells Python where to import the module you plan to use.

The first step in working with files is to open the file using Python's built-in open function.

The open function has two parameters:

The syntax to open a file using the with statement is: "with open([file path]),[mode]) as [variable name]:[execution code]"

Example: with open ("st.txt","w") as f : f.write("Hi from Python!")

As long as it is still within the with statement, the file object can be accessed.

If you want to read a file, you can pass "r" as the second parameter of the open function. Then calling the read method of the file object will return an iterable object containing all the lines of the file.

The suffix of the CSV file is .csv, which uses English commas to separate the data (CSV is the English abbreviation of comma separated values).

CSV files are often used by programmers who need to manage reporting software such as Excel.

Each comma-separated data in the CSV file represents a cell in the report, and each row represents a report row.

Delimiter is a symbol used to separate data in CSV files, such as comma or vertical bar "|".

Read: Access the contents of the file.

Write: Add or modify data in the file.

File path: The location on your computer where the file is stored.

with statement: A compound statement that automatically performs an operation when Python exits the statement.

File object: An object that can be used to read and write files.

CSV file: File with .csv suffix, using commas to separate data. Commonly used in programs that manage reports.

Delimiter: The symbol used to separate data in CSV files, such as commas.

One of the fundamental differences between different programming paradigms is the treatment of state.

State is the value of its internal variables when the program is running.

Global state is the value of the internal global variables of the program when it is running.

Procedural programming: This programming style requires you to write a series of subsidies to solve a problem, each step changing the state of the program.

In procedural programming, we store data in global variables and process it through functions.

Since the state of the program is stored in global variables, problems may arise if the program grows larger.

Procedures are side effects of programming, one of which is changing the state of global variables.

Functional programming: The world's smallest general-purpose programming language.

Functional programming solves the problems that arise in procedural programming by eliminating global state.

Functional programmers rely on functions that do not apply or change global state; the only state they use is the arguments passed to the function.

Advantages and Disadvantages

The object-oriented programming paradigm also solves the problems caused by procedural programming by eliminating global state, but instead of using functions, it uses objects to save state.

A class defines a series of objects that can interact with each other.

Programming paradigm: programming style.

Status: The value of the variables within the program when it is running.

Global state: The value of global variables within the program when it is running.

Procedural programming: This programming style requires writing a series of steps to solve a problem, each step changing the state of the program.

Functional programming: Functional programming eliminates global state through function transfer and solves the problems of procedural programming.

Side effects: changing the value of global variables.

Object-oriented: A programming paradigm that defines objects that can interact with each other.

Class: A means for programmers to classify and group similar objects.

Method: Similar to a function, but it is defined in the class and can only be called on objects created by the class.

Instance: Every object is an instance of a class. Each instance of a class has the same data type as other instances of the class.

Instance variables: Variables that belong to an object.

Magic methods: Methods used by Python in special situations, such as object initialization.

Instantiation of a class: Create a new object using a class.

There are four major concepts in object-oriented programming:

Composition: Through the combination technique, one object is saved as a variable in another object, and the "own" relationship can be modeled.

The four pillars of object-oriented programming: encapsulation, abstraction, polymorphism, and inheritance.

Inheritance: In the genetic inheritance summary, children will inherit characteristics such as eye color from their parents. Similarly, when a class is created, it can inherit methods and variables from another class.

Parent class: The class that is inherited.

Subclass: A class that inherits from a parent class.

Method overriding: A subclass changes the ability to implement methods inherited from the parent class.

Polymorphism: refers to the ability to provide relevant interfaces for different basic forms (data types).

Abstraction: refers to the process of stripping away many characteristics of something so that it retains only its most basic qualities.

Client code: Code outside the applicable object's class.

Encapsulation: Encapsulation includes two concepts. The first concept is that objects in object-oriented programming collect variables (state) and methods (used to change state or perform calculations involving state) in one place - the object itself. The second concept refers to hiding the internal data of a class from direct access by client code.

Combination: Through the combination technique, one object is saved as a variable in another object, and the "own" relationship can be modeled.

In Python, classes are objects. Every class in Python is an instance object of the type class.

There are two types of variables in a class:

If the two objects are the same object, the keyword is returns True, otherwise it returns False.

You can check if a variable is None using the keyword is.