Question

我正在编写一个类，它在“end”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，我得到以下错误 - NameError：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，我道歉

Answer 1

你可以在除了创建它们的函数之外的函数中使用全局变量“by declaring it as global in each function that assigns to it.”

但是，在这种情况下，txt只需要成为该类的成员。

下面的评论，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

您的txt不一定是全局变量。

在您的cnt函数中，只需使用self.txt调用它即可。对于您的打印行功能，请使用count

致电self.count

另一个提示：不要忘记关闭文件。

Answer 3

请勿使用全局变量。

 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 4

我知道你想要使用类，但如果它只计算文件中的行数，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'

定义全局变量的麻烦

4 个答案: