Python：将对象隐式转换为str？ [英] Python: Implicit conversion of object to str?

问题描述

给定以下代码

  A类：
 def __init __（self）：
 self。 b = B（）
 
 def __repr __（self）：
 #return< A with {} inside& ; A with+ repr（self.b）+inside> 
 return< A with+ self.b +inside> ＃TypeError：无法将'B'对象转换为str隐式
 
类B：
 def __repr __（self）：
 return< B& 
 
a = A（）
 print（a）
  

我想知道为什么当添加A的 self.b 到一个字符串时，B __ repr __

• https://docs.python.org/3/reference/datamodel.html#object。 repr


• https://docs.python.org/3/reference/lexical_analysis.html#operators li>
  

解决方案

连接不会导致 self.b 作为字符串求值。您需要明确告诉Python将其强制为字符串。

您可以：

  return< A with+ repr（self.b）+inside> 
  

但是使用 str.format

  return< A with {} inside>。format（self.b）
  

然而，jonrsharpe指出，首先尝试调用 __ str __ 存在），为了使其特别使用 __ repr __ ，有以下语法： {！r} 。

  return< A with {！r} inside>。format（self.b）
  

Given the following code

class A:
  def __init__(self ):
    self.b = B()

  def __repr__(self):
    #return "<A with {} inside>".format( self.b )
    #return "<A with " + repr(self.b) + " inside>"
    return "<A with " + self.b  + " inside>" # TypeError: Can't convert 'B' object to str implicitly

class B:
  def __repr__(self):
    return "<B>"

a = A()
print(a)

I am wondering why B's __repr__ is not called when "adding" A's self.b to a string.

• https://docs.python.org/3/reference/datamodel.html#object.repr
• https://docs.python.org/3/reference/lexical_analysis.html#operators

解决方案

Concatenation doesn't cause self.b to be evaluated as a string. You need to explicitly tell Python to coerce it into a string.

You could do:

return "<A with " + repr(self.b)  + " inside>"

But using str.format would be better.

return "<A with {} inside>".format(self.b)

However as jonrsharpe points out that would try to call __str__ first (if it exists), in order to make it specifically use __repr__ there's this syntax: {!r}.

return "<A with {!r} inside>".format(self.b)

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