Python：变量不在范围内，因为它是实例级变量。未定义全局名称

我正在学习的课程：

import csv
from itertools import islice

class process_csv(object):

    def __init__(self, filename):
        self.filename = filename

    def printfn(self):
        #global filename ??? this is wrong?
        print filename

在解释程序中，我尝试：

Python 2.7.3 (default, Sep 26 2013, 20:08:41) 
[GCC 4.6.3] on linux2
>>> from csv_reader import process_csv
>>> instance1 = process_csv('some_name.csv')
>>> instance1.printfn()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "csv_reader.py", line 11, in printfn
    print filename
NameError: global name 'filename' is not defined

我们非常感谢任何指导方向

解决方案： 下面是我正在处理的代码，其中包含了解决方案。这项工作仍在进行中：

import csv
from itertools import islice

class process_csv(object):

    def __init__(self, filename):
        self.filename = filename

    def printfn(self):
        """ Used for learning how to print the filename :D """
        print self.filename


    def row_count(self):
        """ Returns the csv row_count """
        number_of_rows = len(list(csv.reader(open(self.filename))))
        return number_of_rows

    def read_csv_row(self, row_number):
        """ Returns the contents in row_number """
        try:
            print "Read Row: "+str(row_number)
            with open(self.filename,'rb') as f:
                read_as_csv = csv.reader(f,delimiter='\t', quotechar='"')
                list(islice(read_as_csv,row_number))
                current_row = read_as_csv.next()
        except StopIteration:
            current_row = None
        return current_row


    def assigned_row_titles(self, row_number):
        """ Creates a dictionary with assigned row titles """

        with open(self.filename, 'r') as f:
            current_row = self.read_csv_row(row_number)
            if current_row is not None:
                # EDIT these to suit the format of the csv file
                result = { 'pallet_number' : current_row[0] ,
                           'category' : current_row[1] , 
                           'offer_id_orig' : current_row[2] , 
                           'title' : current_row[3] ,
                           'quantity' : current_row[4] , 
                           'msrp' : current_row[5] ,
                           'offer_id_scanned' : current_row[6] , 
                           'sku' : current_row[7] }
            current_row = None
        return result

    def check_csv_sku(self):
        """ Checks the number of rows that have a sku """
        row_count = self.row_count()
        tot = 0
        tot_read = 0
        tot_skipped = 0
        for row_number in xrange(1,row_count):

            result = self.assigned_row_titles(row_number)
            tot += 1
            if result['sku'] is not "":
                #print str(result)
                tot_read += 1
                ### TODO ###
                # Process the result perhaps add another method like get_item_info_from_website()
            if result['sku'] is "":
                #print 'Skipped: '+str(row_number)
                tot_skipped += 1
                

        print "Total lines read: "+str(tot)
        print "Total lines with sku: "+str(tot_read)
        print "Total lines skipped: "+str(tot_skipped)


if __name__ == '__main__':

    ### (note to self) examples on usage ###
    filename = 'MEE682.csv'
    # create the class instance
    g = process_csv(filename)
    # process the csv and check how many have been processed
    print g.check_csv_sku()
    # read row 14
    print g.read_csv_row(14)
    # read row 18 and assign titles to a dictionary
    print g.assigned_row_titles(18)
    # prints filname
    g.printfn()
    # print the row count
    print g.row_count()

---

filename

不是全局变量。它属于

process\u csv

的一个实例。您可以使用

self.filename

访问它

def printfn(self):
    print self.filename

---

filename

在第一个示例中不是全局变量（或作用域中的变量）。它是类级别的实例级别（类的实例）变量。在

printfn

中，您应该执行以下操作：

def printfn(self):
        print self.filename

---

您的第二个示例之所以有效，是因为当您在贴花

filename

之后立即执行

process\u csv（filename）

时，它就在范围内。

感谢您为我尝试学习的内容提供了术语。我已经读了好几个小时了，然后才来询问堆栈溢出问题。有时这是一个艰难的世界。也许在codereview堆栈交换中这样问会更好。@jmunch：问题是答案中的术语是错误的

filename

不是类级变量，而是实例级变量。@Matthias:类的实例。类级别不是意味着相同吗，还是类级别意味着静态变量？@xbonez:类级别变量在实例之间共享。

def printfn(self):
        print self.filename