Python递归函数不返回值

时间:2014-06-04 10:46:27

标签: python function recursion return-value

这是我在这里提出的第一个问题,所以如果我写了很多东西并且提前多多感谢你看看,我最诚挚的道歉。

问题:

我已经编写了一个函数,如果需要的话,应该调用自己x次,如果不成功则不返回任何内容。但是,当函数似乎成功时,它仍然返回None。

背景:我有许多目录代表2009年的月份。虽然不是所有的月份都存在,但是如果是这种情况,我想上个月,检查该月的目录是否存在如果没有继续在一个月后回到社区,为期6个月。

下面你看到date_tag中的月份09,在我的测试用例中不存在。 08或07都没有。因此函数应该返回06但是它返回None。

import pdb
import generate_months_module
import os

date_tag = '2000/2000/2009/09'
tree_location = '/Users/kelly/Documents/projects/komm/data/directory-tree/'

def iterateOverMonths(date_tag, x):
    if x <= 0:
        return_string = 'no dates found'
        return return_string
    else:
        new_date = generate_months_module.handleDateShifts(date_tag)[1]
        print '\tNEW DATE after calling handleDateShifts' + new_date
        full_path = tree_location + '/' + new_date
        if checkDirectoryExistance(full_path) == True:
            print '\t'+ full_path + ' is a real path'
            return full_path
        else:
            print 'dir does not exist'                                                                                                                       
            iterateOverMonths(new_date, x-1)

def checkDirectoryExistance(dir_path):
    "check if a directory exists, return true or false"
    if os.path.isdir(dir_path) == True:
        return True
    else:
        return False

print iterateOverMonths(date_tag, 6)

generate_months_module.handleDateShifts应该只是获取前一个月并返回它。 (这适用于其他测试用例,所以我非常怀疑问题在这里!)

我的输出是:

6
    NEW DATE after calling handleDateShifts2000/2000/2009/08
    dir does not exist
5
    NEW DATE after calling handleDateShifts2000/2000/2009/07
    dir does not exist
4
    NEW DATE after calling handleDateShifts2000/2000/2009/06

    /Users/kelly/Documents/projects/komm/data/directory-tree/2000/2000/2009/06 is a real path

    returning full path
    None

当我在“return full_path”之前使用pdb.set_trace()时,似乎再次调用该函数DESPITE,IF子句为True,因此写入我想要返回的“full_path”变量。

为什么不返回“/ Users / kelly / Documents / projects / komm / data / directory-tree / 2000/2000/2009/06”路径?

导入功能:

如果有人感兴趣并希望重新创建这个,那么handleDateShifts函数如下(道歉,它有点乱):

def handleDateShifts(corpus_date_string):
    "get background corpus date strings ALSO call this function if month does not exist and need to go back even further"
    century, decade, year, month = corpus_date_string.split('/')
    if month == '01' or month == '02':
        #handle date boundaries which can affect year, decade and cent                                                   
        background_mo_1 = '11'
        background_mo_2 = '12'
        millenium_shift = re.search('[1-9][0][0][0]$', year)
        century_shift = re.search('[1-9][0][0]$', year)
        decade_shift = re.search('[1-9][0]$',year)
        if century_shift or millenium_shift:
            century = int(year) - 100
            decade = int(year) - 10
            year = int(year) - 1
        elif decade_shift:
            decade = int(year) - 10
            year = int(year) - 1
        elif not decade_shift and not century_shift:
            year = int(year) - 1
        background_1_string = str(century) +'/'+ str(decade) +'/'+ str(year) +'/'+ str(background_mo_1)
        background_2_string = str(century) +'/'+ str(decade) +'/'+ str(year) +'/'+ str(background_mo_2)
    else: #the cent/dec/year can stay the same                                                                           
        background_mo_1 = int(month) - 2
    background_mo_2 = int(month) - 1
        if len(str(background_mo_1)) == 1:
            background_mo_1 = '0' + str(background_mo_1)
        if len(str(background_mo_2)) == 1:
            background_mo_2 = '0' + str(background_mo_2)
        background_1_string = str(century) +'/'+ str(decade) +'/'+ str(year) +'/'+ str(background_mo_1)
        background_2_string = str(century) +'/'+ str(decade) +'/'+ str(year)+'/'+ str(background_mo_2)
    return background_1_string, background_2_string

1 个答案:

答案 0 :(得分:1)

您不会在此分支中返回任何内容(结果会丢失):

    else:
        print 'dir does not exist'                                                                                                                       
        iterateOverMonths(new_date, x-1)

如果函数在没有显式return <smth>的情况下运行,则返回None