[英]Sympy __repr__ magic - How does it work?
I noticed that after calling init_printing
method of sympy, variable's representation have a better visual appealing. 我注意到在调用
init_printing
方法之后,变量的表示具有更好的视觉吸引力。 I know that is usually done inheriting repr method. 我知道这通常是继承repr方法。
But when I call __repr__
method, result is different. 但是当我调用
__repr__
方法时,结果是不同的。 Why? 为什么?
Before init_printing
being called, this is the result: 在
init_printing
之前,结果如下:
>>> import sympy as sy
>>> x = sy.Symbol('x')
>>> sy.exp(x)
exp(x)
>> sy.exp(x).__repr__()
'exp(x)'
After init_printing
being called, this is the result: 调用
init_printing
后,结果如下:
>>> import sympy as sy
>> sy.init_printing()
>>> x = sy.Symbol('x')
>>> sy.exp(x)
x
e
>> sy.exp(x).__repr__()
'exp(x)'
Why the repr method doesn't return the same as evaluating the representation of the variable? 为什么repr方法不会像评估变量的表示一样返回?
>>> sy.exp(x).__repr__
<bound method Basic.__repr__ of exp(x)>
That function installs a custom sys.displayhook()
function , which is used in the interactive interpreter to echo the result of expressions: 该函数安装一个自定义的
sys.displayhook()
函数 ,该函数在交互式解释器中用于回显表达式的结果:
sys.displayhook
is called on the result of evaluating an expression entered in an interactive Python session.在评估在交互式Python会话中输入的表达式的结果上调用
sys.displayhook
。 The display of these values can be customized by assigning another one-argument function tosys.displayhook
.可以通过为
sys.displayhook
指定另一个单参数函数来自定义这些值的显示。
The implementation is found in the sympy.interactive.printing
module : 该实现可在
sympy.interactive.printing
模块中找到:
def _init_python_printing(stringify_func, **settings): """Setup printing in Python interactive session. """ import sys from sympy.core.compatibility import builtins def _displayhook(arg): """Python's pretty-printer display hook. This function was adapted from: http://www.python.org/dev/peps/pep-0217/ """ if arg is not None: builtins._ = None print(stringify_func(arg, **settings)) builtins._ = arg sys.displayhook = _displayhook
In other words, this has nothing to do with how the objects implement __repr__
. 换句话说,这与对象如何实现
__repr__
。
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