Python：跟踪For循环的执行 [英] Python: Tracing the Execution of a For Loop

问题描述

我试图跟踪一段包含 for loop 的代码的执行情况，其中包含两个 if条件 。但我需要帮助理解如何在python中执行 for循环。

I am attempting to trace the execution of a piece of code that contains a for loop with two if conditionals. But I need help understanding exactly how for loops are executed in python.

请考虑以下示例：

  numAs = 0
  numEs = 0
  aStr1 = 'abcdefge'
   def someFunc(aString):
1.     for i in range(len(aString)): 
2.           if s[i] == 'a': 
3.               numAs += 1 
4.               continue 
5.           if s[i] == 'e': 
6.               numEs += 1 
7.               if numEs > numAs:  
8.                    break 
9. print(someFunc(aStr1))

问题：使用 aStr 作为参数在上面的代码中第1行执行多少次？

Question: Using aStr as a parameter how many times will line 1 execute in the above code?

我的理解是这段代码的第1行： for i in range（len（aString）），只会被执行一次。第2行和第5行将根据传递的字符串执行多次。当函数遇到 continue 语句时，它会返回到第2行并运行它。请确认或纠正我的想法。

My understanding is that line 1. of this piece of code: for i in range(len(aString)), will only be executed once. While lines 2 and 5 will be executed multiple times depending on the string that is passed. When the function encounters the continue statement it goes back to line 2 and runs it. Please confirm or correct my thinking.

谢谢

推荐答案

您的理解代码的作用是正确的。

Your understanding of what the code does is correct.

FWIW，使用 python -m trace -trace some_script很容易跟踪脚本的执行情况.py 或者你可以看到执行行计数 python -m trace --count some_script.py 。

FWIW, it is easy to follow the execution of a script using python -m trace --trace some_script.py or you can see the execution line counts with python -m trace --count some_script.py.

例如，后者调用 trace 会产生：

For example, the latter call to trace produces:

    1: def someFunc(aString):
            global numAs, numEs
    1:      s = aString
   10:      for i in range(len(aString)): 
    9:            if s[i] == 'a': 
    2:                numAs += 1 
    2:                continue 
    7:            if s[i] == 'e': 
    1:                numEs += 1 
    1:                if numEs > numAs:  
                           break

    1: numAs = 0
    1: numEs = 0
    1: someFunc('flammable')

这篇关于Python：跟踪For循环的执行的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！