2025 Python Beginner Basics Summary (Save Quickly)

1: Introduction:

Python is an interpreted, object-oriented language.

The syntax and dynamic typing of Python, along with the nature of an interpreted language, make it a programming language suitable for scripting and rapid application development on most platforms.

2: Basic Syntax of Python

2.1. Literals

Literals: Fixed values written in the code are called literals.

There are 6 common types of values (data) in Python.

Note: type() statement can be used to check the data type stored in a variable.

2.2. Comments

Single-line comments: Start with #, all text to the right of # is treated as an explanation and is not executed as a program, serving as auxiliary explanation.

Note: It is generally recommended to place a space between the # and the comment content.

Multi-line comments: Enclosed in three double quotes.

2.3. Data Type Conversion

2.4. Identifiers

Identifiers: A series of names used by the user in programming to name variables, classes, methods, etc.

In identifier naming, only the following four types of elements are allowed: English, Chinese, numbers, underscore (_).

Note: It is not recommended to use Chinese, numbers cannot start, and keywords cannot be used.

2.5. Operators

Arithmetic (Mathematical) Operators:

Compound Assignment Operators:

2.6. Strings

2.6.1. Three Ways to Define Strings

Single quote definition: Double quote definition: Triple quote definition:

Among them, the single quote definition can contain double quotes; the double quote definition can contain single quotes; and the escape character (
) can be used to neutralize the quotes, turning them into ordinary strings.

2.6.2. String Concatenation

*Note: **Strings cannot be concatenated with non-string variables.

The default print statement will automatically wrap the output content. In the print statement, adding end=” will output without wrapping.

2.6.3. String Formatting

We can complete quick concatenation of strings and variables using the following syntax:

The following code completes the placement of three different types of variables: strings, integers, and floating-point numbers.

Here, % represents a placeholder. When there is no need to use a variable for data storage, the expression can be directly formatted (the variable’s position is placed in the expression), simplifying the code.

2.6.4. Precision Control of Formatting

We can use the auxiliary symbol “m.n” to control the width and precision of the data.

m controls the width, which must be a number. If the set width is less than the number itself, it will not take effect.

.n controls the decimal precision, which must be a number, and will round to the nearest.

Example: %5d: indicates that the width of the integer is controlled to be 5 digits. For example, the number 11 will become: [space][space][space]11, with three spaces to fill the width.

%5.2f: indicates that the width is controlled to 5, and the decimal precision is set to 2. The decimal point and the decimal part are also counted in the width calculation. For example, when 11.345 is set to %7.2f, the result is: [space][space]11.35. 2 spaces fill the width, and the decimal part is limited to 2 digits of precision, rounded to .35.

%.2f: indicates that there is no width limit, only the decimal precision is set to 2. For example, after setting 11.345 to %.2f, the result is 11.35.

2.6.5. Quick Formatting of Strings

Using the syntax: **f”Content{variable}”** for quick formatting.

Note: This method does not control precision and ignores type.

2.7. Data Input

Using **input()** statement can get input from the keyboard.

Note: Regardless of what type of data is input from the keyboard, the data obtained is always a string type.

Warm reminder: Due to limited space, a packaged folder has been created, and the method of obtaining it is at the end.

3: Python Conditional Statements

3.1. Basic Format of if Statement

The code block belonging to the if judgment must be indented with 4 spaces in the front.

Python determines the affiliation of code blocks through indentation.

3.2. if elif else Statement

4: Python Loop Statements

4.1. while Loop

4.2. for Loop

4.3. range Statement

Used to obtain a sequence of numbers.

5: Python Functions

A function is an organized, reusable code segment that implements a specific function.

Function definition:

Note: If a function does not use the return statement to return data, it will return the literal None; in if judgments, None is equivalent to False; if you define a variable but temporarily do not need it to have a specific value, you can use None as a substitute.

Using global keyword can declare a variable as a global variable inside a function.

6: Python Data Containers

A data type that can contain multiple pieces of data, each piece of data is called an element. Each element can be of any type of data.

Warm reminder: Due to limited space, a packaged folder has been created, and the method of obtaining it is at the end.

6.1. List

Basic syntax:

List methods:

List features:

6.2. Tuple

Basic syntax:

Note: A tuple with only one data must have a comma added after that data.

Tuple methods:

Tuple features:

6.3. String

String methods:

Warm reminder: Due to limited space, a packaged folder has been created, and the method of obtaining it is at the end.

String features:

The string container can only contain a single type, which is the string type.

Strings cannot be modified; if modification is necessary, a new string must be obtained, and the old string cannot be modified.

6.4. Slicing Sequences

Sequences refer to a type of data container that is continuous, ordered, and can be indexed.

Lists, tuples, and strings can all be considered as sequences.

**Syntax:** Sequence[start index:end index:step]

Indicates that from the specified position in the sequence, elements are taken out sequentially until the specified position ends, resulting in a new sequence.

• Start index indicates where to start, can be left blank, which means starting from the beginning.

• End index (not included) indicates where to end, can be left blank, which means taking to the end.

• Step indicates the interval for taking elements.

• The step being negative indicates taking in reverse (note that the start and end indices must also be marked in reverse).

6.5. Set

Basic syntax:

Set methods:

Set features:

Compared to lists, tuples, and strings, sets do not support duplicate elements (they have a built-in deduplication function) and the content is unordered.

6.6. Dictionary

Dictionary definition:

Common operations of dictionaries:

Dictionary features:

• The Key and Value of the key-value pair can be of any type (Key cannot be a dictionary).

• The Key in the dictionary cannot be duplicated; adding a duplicate is equivalent to overwriting the original data.

• Dictionary cannot be indexed by subscript but can retrieve Value through Key.

6.7. General Operations of Data Containers

Comparison of characteristics of data containers:

Common functions of containers:

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