定义全局变量时遇到问题

Question

我正在编写一个类，该类在"结束"行之前读取文件中的行数

class readFile:
    global count
    global txt
    def __init__(self):
        self.count = 0
    def open(self,file):
        self.txt = open(file,"r")
    def cnt(self):
        str = txt.readline()
        while str != "end":
            self.count += 1
            str = txt.readline()
    def printline(self):
        print "the number of lines = %d" % count
    obj = readFile()
    obj.open(raw_input("which file do you want to read? n"))
    obj.cnt()
    obj.printline()

但是当我运行这段代码时，我收到以下错误 -名称错误： 未定义全局名称"txt"

我

正在从java转向python，所以如果有任何风格差异，我深表歉意

Answer 1

您可以在 创建全局变量的函数之外使用全局变量，"通过在分配给它的每个函数中将其声明为 global"。

但是，在这种情况下，txt只需要成为类的成员。

下面内联的评论，以帮助您从Java到Python的旅程...

#!/usr/bin/env python
class ReadFile(object): # Classes have titlecase names and inherit from object
    def __init__(self):
        self.count = 0
        self.txt = None # Initialise the class member here
    def open(self, filename): # file is a Python built-in. Prefer 'filename'
        self.txt = open(filename, "r")
    def cnt(self):
        line = self.txt.readline() # str is a Python built-in. Prefer 'line'.
                                   # Reference the class member with 'self.'
        line = line.strip() # Remove any trailing whitespace
        while line != "end": # TODO: What happens if this line doesn't appear?
            self.count += 1
            line = self.txt.readline().strip()
    def printline(self):
        print "the number of lines = %d" % self.count
obj = ReadFile()
obj.open(raw_input("which file do you want to read? n").strip())
obj.cnt()
obj.printline()
'''
end
'''

Answer 2

只是不要使用全局变量。

 class readFile:
        def __init__(self):
            self.count = 0
        def open(self,file):
            self.txt = open(file,"r")
        def cnt(self):
            str = self.txt.readline()
            while str != "end":
                self.count += 1
                str = self.txt.readline()
        def printline(self):
            print "the number of lines = %d" % self.count

Answer 3

您的txt不需要是全局变量。

在您的 cnt 函数中，只需使用 self.txt 调用它即可。打印行函数的备注相同，使用 self.count 调用 count

另一个提示：不要忘记关闭文件。

Answer 4

我知道

你想使用类，但如果它只是计算文件中的行数，你也可以尝试这样的事情：

with open('test.py') as f:
    l = [x.strip() for x in f.readlines()]
    try: # assuming 'end' is the only word in the line
        print 'the number of lines = {}'.format(len(l[:l.index('end')]))
    except:
        print 'string "end" not found'