Python: Tracing the Execution of a For Loop

问题

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.

Please consider the following example:

  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))

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

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.

Thanks

回答1:

Your understanding of what the code does is correct.

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.

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')

来源：https://stackoverflow.com/questions/8032484/python-tracing-the-execution-of-a-for-loop