Hướng dẫn numeric coercion rules in python - quy tắc cưỡng chế số trong python

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Many programming languages have something called type coercion; it's where the language will implicitly convert one object to another type of object in certain circumstances.

Python does not have type coercion.

Numeric Types and Coercion

If we add together an integer (2) and a floating-point number (3.5) in Python, we'll get back a floating-point number:

>>> x = 2
>>> y = 3.5
>>> x + y
5.5

Python did not coerce the integer into a floating-point number; we don't have type coercion in Python. Instead, Python delegated to the integer and floating point numbers and asked those objects to add themselves together.

Whenever Python sees x + y, it calls the __add__ method on x passing y to it:

>>> x.__add__(y)
NotImplemented

In this case Python got

>>> x.__add__(y)
NotImplemented

>>> x.__add__(y)
NotImplemented

>>> x.__add__(y)
NotImplemented

>>> x.__add__(y)
NotImplemented

>>> x.__add__(y)
NotImplemented

When Python sees this special

>>> x.__add__(y)
NotImplemented

>>> name = "Trey"
>>> x
2
>>> name + x
Traceback (most recent call last):
  File "", line 1, in 
TypeError: can only concatenate str (not "int") to str

This adds the floating-point number to the integer from the right-hand side of the plus sign (

>>> name = "Trey"
>>> x
2
>>> name + x
Traceback (most recent call last):
  File "", line 1, in 
TypeError: can only concatenate str (not "int") to str

>>> name = "Trey"
>>> x
2
>>> name + x
Traceback (most recent call last):
  File "", line 1, in 
TypeError: can only concatenate str (not "int") to str

>>> name = "Trey"
>>> x
2
>>> name + x
Traceback (most recent call last):
  File "", line 1, in 
TypeError: can only concatenate str (not "int") to str

So no type coercion was done here, instead, one of these types of objects knows how to operate with the other type of object when used with the plus operator.

Python Objects Don't Support Type Coercion

A counterexample of this is strings.

What happens if we try to use the

>>> x.__add__(y)
NotImplemented

>>> name = "Trey"
>>> x
2
>>> name + x
Traceback (most recent call last):
  File "", line 1, in 
TypeError: can only concatenate str (not "int") to str

Many programming languages would make the string

>>> name = "Trey"
>>> x
2
>>> name + x
Traceback (most recent call last):
  File "", line 1, in 
TypeError: can only concatenate str (not "int") to str

The reason is that strings in Python don't know how to use the plus operator with numbers and numbers in Python don't know how to use the plus operator with strings, which means our code doesn't work.

So to actually accomplish what we're looking for, we need to explicitly convert the number to a string:

>>> name + str(x)
'Trey2'

We've made a new string out of that number 2, and we're concatenating it to our string

>>> name + str(x)
'Trey2'

Summary

Python don't have type coercion. Python doesn't ever implicitly converts one object to another type of object.

You'll always either rely on at least one of the objects you're working with knowing how to operate with the other type of object or you'll have to explicitly convert one of your objects to another type of object.

Phần này được sử dụng để ghi lại các quy tắc cho sự ép buộc. Khi ngôn ngữ đã phát triển, các quy tắc cưỡng chế đã trở nên khó ghi lại chính xác; Tài liệu về những gì một phiên bản của một triển khai cụ thể là không mong muốn. Thay vào đó, đây là một số hướng dẫn không chính thức liên quan đến sự ép buộc. Trong Python 3.0, sự ép buộc sẽ không được hỗ trợ.

>>> x.__add__(y)
NotImplemented

>>> x.__add__(y)
NotImplemented

>>> name + str(x)
'Trey2'

>>> x.__add__(y)
NotImplemented

>>> name + str(x)
'Trey2'

>>> x.__add__(y)
NotImplemented

>>> name + str(x)
'Trey2'

>>> x.__add__(y)
NotImplemented

>>> name + str(x)
'Trey2'

Sự ép buộc trong Python với ví dụ là gì?

Có loại ép buộc loại trong Python?

Python ép buộc là gì?