我的“ for”循环中的python语法无效

Question

def citypop():
  import csv                                  
  F = open("Top5000Population.txt")           
  csvF = csv.reader(F)
  D = {}
  with csvF for row in csvF:
      city,state,population = row[0],row[1],row[2] 
      population = population.replace(',','') 
      population = int(population)
      city = city.upper()[:12]
      D[(city, state)] = population
  return D

函数citypop()返回一个以(city,state)为键，以该城市（在该州）的人口作为值的字典。

我不断收到语法错误..我不正确理解csv模块吗？

编辑：谢谢您的帮助。...这应该工作，但现在突然我得到了错误

 for city, state, population in reader(F):       File "/Library/Frameworks/Python.framework/Versions/3.3/lib/python3.3/encodings/ascii.py", line 26, in decode         return codecs.ascii_decode(input, self.errors[0]) UnicodeDecodeError: 'ascii' codec can't decode byte 0xa4 in position 7062: ordinal not in range(128)  

当我运行测试用例时..有什么建议吗？

Answer 1

当您尝试与statement一起使用时，您认为您的意思是这样-在这种情况下，文件将在其下保留代码后立即关闭：

from csv import reader

def citypop():
  D = {}
  with open("Top5000Population.txt") as F:
    for city, state, population in reader(F):
      city = city.upper()[:12]
      D[(city, state)] = int(population.replace(',',''))
  return D

要么：

def citypop():
  with open("Top5000Population.txt") as F:
    return dict(((x.upper()[:12], y), int(z.replace(',', '')) for x, y, z in reader(F))

Answer 2

我认为您误解了Python的with语句 。 制作第6行：

for row in csvF:

应该解决问题。

作为参考， with语句与C＃中的using语句基本相同； 它声明了完成后需要卸载或释放的资源范围。