CS 61A 2018 Python学习要点记录 Chapter1

这门课程的学习主要是在reading中完成的，视频讲解也穿插在了reading中
故按照CS 61A 2018的参考书的章节作为分段，记录章节的重点信息

之前的内容比较简单，故本章从1.5节开始记录

1.5 Control
reading的网址：http://composingprograms.com/pages/15-control.html
1.5.1 Statements
Control statements are statements that control the flow of a program's execution based on the results of logical comparisons.
Statements differ fundamentally from the expressions that we have studied so far. They have no value. Instead of computing something, executing a control statement determines what the interpreter should do next.
statement与expression的区别：
If you want to do something with the result of an expression, you need to say so: you might store it with an assignment statement or return it with a return statement.
1.5.2 Compound Statements
A compound statement is so called because it is composed of other statements.
a header and an indented suite of statements is called a clause. A compound statement consists of one or more clauses:

1.5.3 Defining Functions II: Local Assignment
The effect of an assignment statement is to bind a name to a value in the first frame of the current environment. As a consequence, assignment statements within a function body cannot affect the global frame.

1.5.4 Conditional Statements
Conditional statements：
When executing a conditional statement, each clause is considered in order. The computational process of executing a conditional clause follows.
1）Evaluate the header's expression.
2）If it is a true value, execute the suite. Then, skip over all subsequent clauses in the conditional statement.

Boolean contexts

1.5.5 Iteration
例子：斐波那契数列

# sequence of Fibonacci numbers # 斐波那契数列由 0 和 1 开始，之后的斐波那契数就是由之前的两数相加而得出。 # F(1)=0, F(2)=1,F(3)=1,... # 0 1 1 2 3 5 8 13 def Fibonacci(n):     if (n==0 or n==1):         return n     pred, curr = 0, 1     k = 2        while(k < n):         curr, pred = pred + curr, curr  # 或者 pred, curr = curr, pred + curr         k = k + 1     return curr  print(Fibonacci(5)) 

notes:
A while statement that does not terminate is called an infinite loop. Press -C to force Python to stop looping.

1.5.6 Testing
Assertions
When the expression being asserted evaluates to a true value, executing an assert statement has no effect. When it is a false value, assert causes an error that halts execution.
例子：

Doctests文档测试
Python provides a convenient method for placing simple tests directly in the docstring of a function.
the first part：contain a one-line description of the function + a blank line
the second part: a detailed description of arguments and behavior
the third part: a sample interactive session that calls the function

有关 doctests Module的介绍：https://blog.csdn.net/qq_40061206/article/details/109074188

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notes:

• range()
  range(start, stop[, step])
  start: 计数从 start 开始。默认是从 0 开始。例如range（5）等价于range（0， 5）
  stop: 计数到 stop 结束，但不包括 stop。例如：range（0， 5） 是[0, 1, 2, 3, 4]没有5
  step：步长，默认为1。例如：range（0， 5） 等价于 range(0, 5, 1)
  range一般是三个参数，最后的1通常省略，前闭后开

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