python:正确使用全局变量

Question

这是代码!

import csv

def do_work():
      global data
      global b
      get_file()
      samples_subset1()
      return

def get_file():

      start_file='thefile.csv'

      with open(start_file, 'rb') as f:
        data = list(csv.reader(f))
        import collections
        counter = collections.defaultdict(int)

      for row in data:
        counter[row[10]] += 1
      return

def samples_subset1():

      with open('/pythonwork/samples_subset1.csv', 'wb') as outfile:
          writer = csv.writer(outfile)
          sample_cutoff=5000
          b_counter=0
          global b
          b=[]
          for row in data:
              if counter[row[10]] >= sample_cutoff:
                 global b
                 b.append(row) 
                 writer.writerow(row)
                 #print b[b_counter]
                 b_counter+=1
      return

我是python的初学者.我的代码运行的方式是我调用do_work,do_Work将调用其他函数.这是我的问题:

1. 如果我需要data只被2个函数看到我应该让它全球化吗？如果不是那么我应该如何打电话samples_subset1？我应该来自get_file还是来自do_work？

2. 代码有效,但是你可以指出其编写方式的其他好/坏事吗？

3. 我正在处理一个csv文件,有多个步骤.我正在将步骤分解为不同的功能,例如get_file,samples_subset1还有更多我将添加的功能.我应该继续这样做我现在这样做我在这里打电话给每个人的功能do_work吗？

这是新代码,根据下面的答案之一:

import csv
import collections

def do_work():
      global b
      (data,counter)=get_file('thefile.csv')
      samples_subset1(data, counter,'/pythonwork/samples_subset1.csv')
      return

def get_file(start_file):

        with open(start_file, 'rb') as f:
        global data
        data = list(csv.reader(f))
        counter = collections.defaultdict(int)

      for row in data:
        counter[row[10]] += 1
      return (data,counter)

def samples_subset1(data,counter,output_file):

      with open(output_file, 'wb') as outfile:
          writer = csv.writer(outfile)
          sample_cutoff=5000
          b_counter=0
          global b
          b=[]
          for row in data:
              if counter[row[10]] >= sample_cutoff:
                 global b
                 b.append(row) 
                 writer.writerow(row)
                 #print b[b_counter]
                 b_counter+=1
      return

Answer 1

根据经验,避免全局变量.

这里很简单:让get_file返回数据,然后你可以说

data = get_file()
samples_subset1(data)

另外,我会在文件顶部执行所有导入操作