如何在 python "recursive" 函数中重置全局变量？

Question

def getValueForSpecificKey(self,capturedLog,key):

     ''' Get value from log for any specific key,caputredLog must be a string'''
     global Found
     global returnValue
     if type(capturedLog)==type({}):
         for eachKey in capturedLog:
             if eachKey==key:
                 Found=True
                 print "Found Key Match :",eachKey
                 print capturedLog[key]
                 listAppendValue=capturedLog[key]
                 #returnValue=capturedLog[key]
                 returnValue.append(listAppendValue)
                 print "="*1000
                 print "The value for key in the captured Log is -> ",capturedLog[key]
                 print " Return value "*10,(returnValue)
                 return Found,returnValue
             self.getValueForSpecificKey(capturedLog[eachKey],key)
     elif type(capturedLog) is list:
         for elements in capturedLog:
             self.getValueForSpecificKey(elements,key)
     print returnValue
     return Found,returnValue

我有这个函数递归迭代一个有效的 json.The json 可能包含 dict 或 list.The 函数在这里搜索需要一些输入日志，它是 json 和一个在 json.I 中搜索的密钥能够迭代以获取 json 中的所有密钥。一切都很好。

但是当我尝试 return value.Since returnValue 是一个全局变量时，问题就来了。追加到列表中，继续将所有值追加到相同的list.Even 当我从其他模块创建 class 的对象并调用此函数时，列表仍在增长，我无法 clear/reset returnValue before/after 函数 call.I 需要更改 returnValue ，它是每次从外部模块创建对象时的列表，即当第一次这个函数是 called.So 时，这是一个问题我需要用递归 return 值。

由于api已经定义了我只能更改其中的代码。

请帮忙。谢谢

Answer 1

def getValueForSpecificKey(self,capturedLog,key,first=[])
global returnaValue
if not first:
   first.append(1)
   returnaValue = []

这将在您第一次调用时创建一个全局空列表。这将指示您应该清除全局列表 returnValue。无 api 更改并使用递归

Answer 2

我认为您应该将递归函数更改为不需要任何全局变量。如果你只希望找到一个结果，我认为它并不太复杂。

def getValueForSpecificKey(self, capturedLog, key):
    '''
    Get value from log for any specific key.
    capturedLog will be searched if it is a list or dictionary.
    Returns None if the key is not found, or capturedLog is another type.
    '''

    if isinstance(capturedLog, dict):
        if key in capturedLog:                # base case #1 (found the key)
            return capturedLog[key]

        values = capturedLog.values()

    elif isinstance(capturedLog, list):
        values = capturedLog

    else:
        return None                           # base case #2 (not a list or dict)

    for value in values:
        result = self.getValueForSpecificKey(value, key)      # recursive case
        if result is not None:
            return result

    return None                               # nothing found in the recursive search

如果您可能在不同的字典中有多个具有所需键的值，您可能需要传递一个列表：

def getValueForSpecificKey(self, capturedLog, key, results=None):
    '''
    Get value from log for any specific key.
    capturedLog will be searched if it is a list or dictionary.
    Returns an empty list if the key is not found, or capturedLog is another type.
    '''
    if results is None:
        results = []               # start a new list if this is a non-recursive call

    if isinstance(capturedLog, dict):
        if key in capturedLog:
            results.append(capturedLog[key])     # found a result, add it to the list
            return results

        values = capturedLog.values()

    elif isinstance(capturedLog, list):
        values = capturedLog

    else:
        return results

    for value in values:  # recursive calls will add to the results list as necessary
        self.getValueForSpecificKey(value, key, results)

    return results

Answer 3

好的，这是解决方案

在执行函数定义时评估默认参数值。这意味着在定义函数时表达式被计算一次，并且每次调用都使用相同的“预计算”值。当默认参数是可变对象（例如列表或字典）时，理解这一点尤为重要：如果函数修改了对象（例如，通过将项目附加到列表），则默认值实际上被修改了。这通常不是预期的。解决这个问题的一种方法是使用 None 作为默认值，并在函数体中显式测试它，例如：

def getValueForSpecificKey(self,capturedLog,key,First=None):

     ''' Get value from requests log for any specific key,caputredLog must be a string'''
     global Found
     global returnValue
     if First is None:
         First='notnone'
         Found=False
         returnValue=[]
         print "Return Value ->",returnValue
         print "Found - >",Found

     if type(capturedLog)==type({}):
         for eachKey in capturedLog:
             print eachKey
             if eachKey==key:
                 Found=True
                 print "Found Key Match :",eachKey
                 print capturedLog[key]
                 listAppendValue=capturedLog[key]
                 returnValue.append(listAppendValue)
                 print "="*1000
                 print "The value for key in the captured Log is -> ",capturedLog[key]
                 print " Return value "*10,(returnValue)
                 return Found,returnValue
             print "CapturedLog - >",capturedLog
             print "Calling using recursion "
             self.getValueForSpecificKey(capturedLog[eachKey],key,First)
     elif type(capturedLog) is list:
         for elements in capturedLog:
             self.getValueForSpecificKey(elements,key,First)
     return Found,returnValue

如何在 python "recursive" 函数中重置全局变量？

How to reset a global variable in python "recursive" function?

python

recursion

json