Python 全局变量在某些函数中更改，但在循环中其他函数没有更改

Question

我确信以前有人回答过类似的问题，但这些帖子似乎已经在有关全局变量和循环的更受欢迎的问题中消失了。

我正在尝试编写一个循环来逐步执行 Google Analytics API，每天提取数据。我确信已经有一些包可以做到这一点，但这对我来说是一种学习体验。

我卡住的地方是我的循环似乎在进行正确的天数，但是发送到 GA Reporting API (V4) 的实际请求并未使用全局变量进行更新，即使是简单的打印() 似乎表明它确实更新了。

这是我的代码：

# Reporting API V4

from apiclient.discovery import build
from oauth2client.service_account import ServiceAccountCredentials

# Import JSON
import json

# Open JSON config file
jsonConfig = open("config.json", "r")

# Parse the JSON file
configRead = json.loads(jsonConfig.read())

# Define global vars

SCOPES = ['https://www.googleapis.com/auth/analytics.readonly']
KEY_FILE_LOCATION = configRead['keyFileLocation']
VIEW_ID = 12345678 # made up for this exercise

startDate = 732
endDate = 732

# Define report #1
request1 = {
        'reportRequests': 
        [
          {
            'viewId': VIEW_ID,
            'dateRanges': 
            [
              {
                'startDate': f'{startDate}daysAgo',
                'endDate': f'{endDate}daysAgo'
              }
            ],
            'metrics': 
            [
              {
                'expression': 'ga:sessions'
              }
            ],
            'dimensions': 
            [
              {
                'name': 'ga:date'
              }
            ],
            'pageSize': 1
          }
        ]
      }

def initialize_analyticsreporting():
  # Initializes an Analytics Reporting API V4 service object.
  # Returns: An authorized Analytics Reporting API V4 service object.

  credentials = ServiceAccountCredentials.from_json_keyfile_name(
      KEY_FILE_LOCATION, SCOPES)

  # Build the service object
  analytics = build('analyticsreporting', 'v4', credentials=credentials)

  return analytics


def get_report(analytics):
  # Queries the Analytics Reporting API V4.
  # Args: _ analytics _ : An authorized Analytics Reporting API V4 service object.
  # Returns: The Analytics Reporting API V4 response.
  global startDate
  global endDate
  global request1

  return analytics.reports().batchGet(
      body=request1
      ).execute()

def print_response(response):

  # Parses and prints the Analytics Reporting API V4 response.
  # Args: _ response _ : An Analytics Reporting API V4 response.

  for report in response.get('reports', []):
    columnHeader = report.get('columnHeader', {})
    dimensionHeaders = columnHeader.get('dimensions', [])
    metricHeaders = columnHeader.get('metricHeader', {}).get('metricHeaderEntries', [])

    for row in report.get('data', {}).get('rows', []):
      dimensions = row.get('dimensions', [])
      dateRangeValues = row.get('metrics', [])

      for header, dimension in zip(dimensionHeaders, dimensions):
        print(header + ': ', dimension)

      for i, values in enumerate(dateRangeValues):
        for metricHeader, value in zip(metricHeaders, values.get('values')):
          print(metricHeader.get('name') + ':', value)


def main():
  global startDate
  global endDate

  analytics = initialize_analyticsreporting()
  while startDate >= 725:
    response = get_report(analytics)
    print(f'{startDate}daysAgo')
    print_response(response)
    startDate -= 1
    endDate -= 1
  print("Done now, cheers")

if __name__ == '__main__':
  main()

在那个具体的例子中，当它循环时，它会在 request1 中更新 startDate 和 endDate。

目前的输出：

732daysAgo
ga:date:  20181123
ga:sessions: 2887
731daysAgo
ga:date:  20181123
ga:sessions: 2887
730daysAgo
ga:date:  20181123
ga:sessions: 2887
729daysAgo
ga:date:  20181123
ga:sessions: 2887
728daysAgo
ga:date:  20181123
ga:sessions: 2887
727daysAgo
ga:date:  20181123
ga:sessions: 2887
726daysAgo
ga:date:  20181123
ga:sessions: 2887
725daysAgo
ga:date:  20181123
ga:sessions: 2887
Done now, cheers

知道可能是什么问题吗？

Answer 1

问题是您希望根据startDate 和endDate 的值动态生成request1，但您目前只在程序开头定义一次request1，所以它永远不会根据其中任一变量更改其定义。

要让request1 是动态的，您可以创建一个返回请求的函数：

startDate = 732 
endDate = 732
VIEW_ID = 12345678

def get_request1():
    global startDate
    global endDate
    global VIEW_ID
    
    return {
    'reportRequests': 
    [
      {
        'viewId': VIEW_ID,
        'dateRanges': 
        [
          {
            'startDate': f'{startDate}daysAgo',
            'endDate': f'{endDate}daysAgo'
          }
        ],
        'metrics': 
        [
          {
            'expression': 'ga:sessions'
          }
        ],
        'dimensions': 
        [
          {
            'name': 'ga:date'
          }
        ],
        'pageSize': 1
      }
    ]
  }

因此，每次调用get_request1()，其返回值将始终包含当前的开始日期和结束日期。