Python 嵌套读写器不重置

我有嵌套的DictReader迭代器，但我注意到，对于内置建筑，在位置中的行，中的

每次迭代后都不会重置，这导致它仅在第一次迭代后将其与建筑中的最后一个对象进行比较。为什么不复位

import csv

building = csv.DictReader(open('tblBuilding.csv', newline=''), delimiter=',', quotechar='"')
purpose = csv.DictReader(open('tblPurpose.csv', newline=''), delimiter=',', quotechar='"')
room = csv.DictReader(open('tblRoom.csv', newline=''), delimiter=',', quotechar='"')
location = csv.DictReader(open('Locations.csv', newline=''), delimiter=',', quotechar='"')

data, i = {}, 0

for row in location:
    result = {}
    for build in building:
        if row['Build'] == build['BuildingName']:
            result['BuildingID'] = build['BuildingID']

它们不会重置，因为基础文件对象不会重置。您可以再次将文件倒回起始位置，但要考虑到第一行是标题行，因此也可以跳过该行：

building_file = open('tblBuilding.csv', newline='')
building = csv.DictReader(building_file, delimiter=',', quotechar='"')


for row in location:
    result = {}
    for build in building:
        if row['Build'] == build['BuildingName']:
            result['BuildingID'] = build['BuildingID']
    building_file.seek(0)  # rewind the underlying file object to the start again
    next(building)  # skip header row

但是首先，您不应该在嵌套的CSV文件上循环。在处理位置之前，将建筑信息存储在字典中：

with open('tblBuilding.csv', newline='') as building_file:
    building = csv.DictReader(building_file, delimiter=',', quotechar='"')
    buildings = {b['BuildingName']: b['BuildingID'] for b in building}

buildings
字典现在将
BuildingName
映射到
BuildingID
值。现在，您可以在O（1）恒定时间内查找建筑物，而不必在每个位置的所有CSV行上循环：

为什么会“重置”？为什么不会？我认为，就像嵌套for循环一样，每次外部循环运行时，内部循环从头到尾都会运行。但是（很明显！）这并不总是正确的-这取决于在循环中迭代的内容。请参见，谢谢你的解释！
for row in location:
    result = {}
    building_id = buildings.get(row['Build'])
    if building_id:
        result['BuildingID'] = building_id