python中定义变量的问题

Question

我试图通过这段代码编写一些xml，

docs = XmlReportGenerator()
docs.AddMatchRow('FC Barcelona','Madryt','5:0')
docs.Save()

并且编写了自己的方法：

from lxml import etree

class XmlReportGenerator:
    """"""
    root = etree.Element('results')
    doc = etree.ElementTree(root)

    #----------------------------------------------------------------------
    def __init__(self):

        """""" 

    def AddMatchRow(self,teamA,teamB, score):
        pageElement = etree.SubElement(root,'Flight',teamA, teamB, score)

        """"""

    def Save(self,path = None):
        outFile = open('Matches.xml', 'w')
        doc.write(outFile) 

NameError: global name 'root' is not Defined 进程终止，退出代码为 1 完成

名称错误：未定义全局名称“doc” 进程终止，退出代码为 1 完成

我错过了什么吗？我是 python 的新手（我在 c# 方面有更多经验）。

Answer 1

Python 是明确的。实例变量必须以 self. 开头。类变量必须前面加上类的名称。

这是一个固定版本。原始的 SubElement 调用也不正确：

from lxml import etree

# derive from 'object' if Python 2.X (it is default in Python 3.X)
class XmlReportGenerator(object):

    def __init__(self):
        # clearer to init instance variables here.
        self.root = etree.Element('results')
        self.doc = etree.ElementTree(self.root)

    def AddMatchRow(self,teamA,teamB, score):
        # Need self.root here
        pageElement = etree.SubElement(self.root,'Flight')
        # Added data elements (or did you want attributes?)
        etree.SubElement(pageElement,'teamA').text = teamA
        etree.SubElement(pageElement,'teamB').text = teamB
        etree.SubElement(pageElement,'score').text = score

    def Save(self,path = None):
        outFile = open('Matches.xml', 'w')
        # Need self.doc here
        self.doc.write(outFile)

# This code will run if the script is executed directly,
# but will be skipped if the script is imported by another script.
if __name__ == '__main__':
    docs = XmlReportGenerator()
    docs.AddMatchRow('FC Barcelona','Madryt','5:0')
    docs.Save()

Answer 2

self 的存在是有原因的。使用self.root，而不是root