Chapter1-2

0. Programming

What is Programming Language? 什么是编程语言？

Programming language like a code for writing the instructions the computer will follow
编程语言就像是编写计算机指令的代码

Syntax and Semantics 语法和语义

Syntax语法: the precise form of every structure in programming language
Semantics语义: the precise meaning of every structure in programming language

True or False? The syntax of a language is its meaning, and semantics is its form

Answer: False ❌ (Syntax is form, semantics is meaning)

1. High-level vs Low-level Languages 高级语言 vs 低级语言

High-level computer languages 高级计算机语言

Designed to be used and understood by humans
Example: c = a + b

Low-level language 低级语言

Computer hardware can only understand machine language
Example: Load numbers, add in CPU, store result

选择题 Which one?
Computer languages designed to be used and understood by humans are:

a) natural languages

b) high-level computer languages ✅

c) machine languages

d) fetch-execute languages

2. Compilers vs Interpreters 编译器 vs 解释器

Compilers 编译器

Convert programs into machine language all at once
一次性将程序转换为机器语言
Compiled programs run faster 编译的程序运行更快

Interpreters 解释器

Analyze and execute source code instruction by instruction
逐条分析和执行源代码
More flexible programming environment 更灵活的编程环境

3. What is python？ Python是啥？

python for python language and the interpreter

python是一种解释型语言，使用python解释器执行代码
python解释器可以在不同平台上运行，如windows、linux、mac等
python解释器的版本有很多种，如python2、python3等

python is a general-purpose language

python是一种通用型语言，可用于开发各种应用程序
python的语法简单易学，适合初学者
domain-specific language：HTML,JS,Matlab…

dynamic language or static language?

python is a moden dynamic language
python 既是动态语言，也是静态类型语言?

python is open source

python是一种开源语言，用户可以自由使用、修改和分发python代码

features of Python - Syntax Characteristics句法特征

Readability
Simplicity

4. Python development environment Python开发环境

Python official website: https://www.python.org/

True or False? A programming environment refers to a place where programmers work.
Answer: True ✅

What is IDLE?

IDLE是python的集成开发环境，提供了一个简单的编辑器和调试器

Script Mode or Interactive Mode

IDLE提供了两种运行python代码的方式：脚本模式和交互式模式

脚本模式用于执行python脚本文件，交互式模式用于在IDLE中直接输入和执行python代码

Anaconda: 数据科学Python发行版

Anaconda是一个用于数据科学的python发行版，提供了许多常用的python库和工具

安装Anaconda后，用户可以直接使用其中的python解释器和开发环境

自带Jupyter Notebook

https://www.anaconda.com/

more IDE

除了IDLE，还有许多其他的python开发环境，如PyCharm、Visual Studio Code等

这些开发环境提供了更多的功能和工具，如代码自动补全、调试器、版本控制等

顺手即可

5. Python program

Function 函数

def <function_name>(<parameters>):
	"""docstring"""
	<statement(s)>

函数定义以def关键字开头，后面跟着函数名、参数列表和冒号
函数体缩进4个空格
函数可以有参数，也可以没有参数
函数可以有返回值，也可以没有返回值
函数可以有文档字符串，用于描述函数的功能和参数('''或者"""均可)

Parameters 参数

>>> def greet(person):
        print("Hello", person)
        print("How are you?")
 
>>> greet("Terry")
Hello Terry
How are you?

Comments 注释

# Single line comments 单行注释
'''...''' or """...""" Multiple line comments 多行注释

Indentation 缩进

Uses whitespace to indicate code structure 使用空格表示代码结构
Replaces traditional symbols like {}

6. Basic methods of writing programs

IPO Framework IPO框架

Input输入: the beginning of a program 程序开始
Process处理: computes incoming data 计算输入数据
Output输出: displays the result 显示结果

Software development process 软件开发流程

软件开发过程包括需求分析、设计、编码、测试和维护等阶段

Analyze the Problem分析问题
Determine Specifications确定规格 - what it will do
Create a Design创建设计 - how it will work
Implement the Design实现设计
Test/Debug测试/调试
Maintain维护

True or False Questions:

The best way to write a program is to immediately type in some code and then debug it until it works.

False ❌ (应该先分析设计)

An algorithm can be written without using a programming language.

True ✅ (可以用伪代码)

Programs no longer require modification after they are written and debugged.

False ❌ (程序需要持续维护)

Variables and Identifiers 变量和标识符

Names are given to identify variables, functions, classes, etc. 标识符是用于标识变量、函数、类等的名称

Rules规则:

Must begin with letter or underscore 必须以字母或下划线开头
Followed by letters, digits, or underscores 后面可以是字母、数字或下划线
Case sensitive 区分大小写

标识符不能使用python的保留字(reserved words/keywords) 例如：if、else、while、for、def、class、True、False、None等
标识符不能使用python的Built-in Functions 例如：print、input、eval、type、len等

Keywords 关键词

Reserved words that cannot be used as variable names 保留字，不能用作变量名

Expressions 表达式

Fragments of code that produce new data values 产生新数据值的代码片段

Components组成:

Literals字面量: 3.9, 1, "Hello"
Variables变量
Operators运算符: +, -, *, /, **

示例：

算术表达式：2 + 3、x * y
函数调用表达式：len(my_list)

Assignment赋值

x = 3.9 * x * (1-x)
fahrenheit = 9/5 * celsius + 32

Variable assignment models变量赋值模型:

Sticky-note model 便利贴模型 ✅
Variable-as-box model 变量作为盒子模型

Simultaneous Assignment同时赋值

sum, diff = x+y, x-y
x, y = y, x  # Swap values交换值

7. Definite Loops(有限循环)

for i in range(10):
    print(i)
 
for i in [1,2,3,4,5]:
    print(i)
 
for i in "hello":
    print(i)

range()函数

Range Function range函数

>>> list(range(10))
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

8. Input and Output 输入输出(IO)

input()

a = input('Please enter a number:')  # 返回字符串

input()函数用于从用户获取输入

函数返回一个字符串

print()

print(3+4)                    # 7
print(3, 4, 3+4)             # 3 4 7
print("The answer is", 3+4)   # The answer is 7

eval()函数

可以使用eval()函数将字符串转换为其他类型

Evaluates strings as Python expressions
本质是将字符串作为Python表达式求值（有风险）

也可以使用int()、float()等函数将字符串转换为整数或浮点数

>>> eval("1+3")
4
>>> eval("print('hello')")
hello

9. Summary总结

Key Concepts关键概念

Rules of Python: comments, indentation Python规则：注释、缩进
IPO framework IPO框架
Software Development Process 软件开发流程
Identifiers, Expressions, Statements 标识符、表达式、语句
Loops 循环
IO 输入输出

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