Python追加到类中打开的文件

Question

这是我的 Python 代码。我正在尝试创建一个执行文件的类 操纵。我使用了与 URL 类似的结构，但我无法附加到文件中。

add_to_file.py-----------

import os
import sys

class add_to_file(object):
    def __init__(self, filename):
        self.data_file = open(filename,'a')
    def __enter__(self):  # __enter__ and __exit__ are there to support
        return self       # `with self as blah` syntax
    def __exit__(self, exc_type, exc_val, exc_tb):
        self.data_file.close()
    def __iter__(self):
        return self
    def __append__(s):
        self.data_file.write(s)
    __append__("PQR")

add_to_file("Junk")

---

结果-------

Traceback (most recent call last):
  File "add_to_file.py", line 4, in <module>
    class add_to_file(object):
  File "add_to_file.py", line 15, in add_to_file
    __append__("PQR")
  File "add_to_file.py", line 14, in __append__
    self.data_file.write(s)
NameError: global name 'self' is not defined

Answer 1

将def __append__(s): 更改为def __append__(self, s):

Answer 2

目前还不清楚您到底想要完成什么——它看起来有点像上下文管理器类。我将__append__() 重命名为append()，因为以双下划线开头和结尾的方法只能由语言定义，并且我根据PEP 8 - Style Guide for Python Code 将您的类从add_to_file 重命名为AddToFile。

import os
import sys

class AddToFile(object):
    def __init__(self, filename):
        self.data_file = open(filename,'a')
    def __enter__(self):  # __enter__ and __exit__ are there to support
        return self       # `with self as blah` syntax
    def __exit__(self, exc_type, exc_val, exc_tb):
        self.data_file.close()
    def __iter__(self):
        return self
    def append(self, s):
        self.data_file.write(s)


with AddToFile("Junk") as atf:
    atf.append("PQR")

with open("Junk") as file:
    print(file.read())  # --> PQR