python错误__str__返回NoneType

Question

class Pixel:
  """Representing a 'pixel' aka one character on the screen
  is mostly gonne be used in Map using a tuple location and a
  character that can be changed"""

  def __init__(self, char='#', location=(0,0)):
    assert type(char) == str
    assert type(location[0]) == int and type(location[1]) == int
    self.location = location
    self.x = self.location[0]
    self.y = self.location[1]
    self.char = char

  def __str__(self):
    return(self.char)



class Map:
  """Representing a map by having diffferent characters
  on different lines and being able to manipulate the 
  characters, thus playing a game"""

  def __init__(self, file=None):
    self.pixels = {}
    if not file:
      self.rows = 3
      self.colls = 3
      for r in range(self.rows):
        for c in range(self.colls):
          self.pixels[(r, c)] = Pixel('#', (r, c))

  def __str__(self):
    print(self.pixels)
    for c in range(self.colls):
      print('')
      for r in range(self.rows):
        print(self.pixels[(r, c)], end='')





a = Map()
print(a)

我正在尝试创建一个定义网格的类，其中网格中的每个位置都有一个字符，但是当我运行代码时，我收到一个错误，告诉我__str__返回一个NoneType。我知道我在启动Map时还没有处理文件输入，但这不是问题所在，这是我得到的输出。

{(0, 1): <__main__.Pixel object at 0x7f31612a3080>,
 (1, 2): <__main__.Pixel object at 0x7f31612a3470>,
 (0, 0): <__main__.Pixel object at 0x7f31612a3048>,
 (2, 0): <__main__.Pixel object at 0x7f31612a34a8>,
 (1, 0): <__main__.Pixel object at 0x7f31612a32b0>,
 (2, 2): <__main__.Pixel object at 0x7f31612a3390>,
 (0, 2): <__main__.Pixel object at 0x7f31612a30b8>,
 (2, 1): <__main__.Pixel object at 0x7f31612a3358>,
 (1, 1): <__main__.Pixel object at 0x7f31612a32e8>}

###
###
###Traceback (most recent call last):
  File "main.py", line 45, in <module>
    print(a)
TypeError: __str__ returned non-string (type NoneType)
exited with non-zero status

我也很困惑，为什么来自__str__的{​​{1}}中的字母将我引用到Map个对象而不是使用__main__.Pixel方法，但这可能只是我的缺乏知识

我错过了什么？

Answer 1

您应该使用__repr__。同样在Map.__str__，你没有返回任何东西。对于前

In [10]: class Test:
   ....:     def __str__(self):
   ....:         return "str"
   ....:     def __repr__(self):
   ....:         return "repr"
   ....:     

In [11]: t=Test()

In [12]: t
Out[12]: repr

In [13]: print(t)
str

Answer 2

我忘记了document.getElementById("trsScript").style.webkitTransform = `rotate(${x}deg)` 任何事情，我已经return打印了我需要的所有内容，但我没有为__str__返回任何内容，因此我收到了NoneType错误。< / p>