看看Python 官网的文档 whatsnew,Python 3.10 已然距离我们越来越近了,然我们看看 Python 3.10 相较于 Python 3.9 有哪些改变吧
新特性
通过括号来组织多个上下文管理器
**的福音,以前在面对有多个上下文管理器时,我们只能采取多层嵌套的方式,像这样:
with open("read.txt", "r") as rfile:
with open("write.txt", "w") as wfile:
wfile.write(rfile.read())
会不会变成这样,[捂脸][捂脸][捂脸]
那在 Python3.10 中,我们可以这样写了:
with (
open("read.txt", "r") as rfile,
open("write.txt", "w") as wfile
):
wfile.write(rfile.read())
更加友好的错误信息
语法错误
- 对于代码中
未闭合括号或引号
造成的语法错误,解释器可以提供具体出错的开头位置
比如下面这段错误代码(是因为大括号没有闭合):
# filename: syntax_error_1.py
expected = {9: 1, 18: 2, 19: 2, 27: 3, 28: 3, 29: 3, 36: 4, 37: 4,
38: 4, 39: 4, 45: 5, 46: 5, 47: 5, 48: 5, 49: 5, 54: 6,
some_other_code = foo()
Python 3.9 版本运行的报错信息,很难定位到错误原因:
> C:\Users\zioyi\.pyenv\pyenv-win\versions\3.9.6\python.exe syntax_error_1.py
File "C:\Users\zioyi\python_code\syntax_error_1.py", line 3
some_other_code = foo()
^
SyntaxError: invalid syntax
再来看看 Python 3.10 的报错信息,就显得贴心很多了:
> C:\Users\zioyi\.pyenv\pyenv-win\versions\3.10.0b4\python.exe syntax_error_1.py
File "C:\Users\zioyi\python_code\syntax_error_1.py", line 1
expected = {9: 1, 18: 2, 19: 2, 27: 3, 28: 3, 29: 3, 36: 4, 37: 4,
^
SyntaxError: '{' was never closed
- 对于语法错误,解释器将
高亮
显示构成语法错误代码的完整错误范围
先看一下 Python 3.9:
>>> foo(x, z for z in range(10), t, w)
File "<stdin>", line 1
foo(x, z for z in range(10), t, w)
^
SyntaxError: Generator expression must be parenthesized
再看一下 Python 3.10:
>>> foo(x, z for z in range(10), t, w)
File "<stdin>", line 1
foo(x, z for z in range(10), t, w)
^^^^^^^^^^^^^^^^^^^^
SyntaxError: Generator expression must be parenthesized
原来,^^^^^^^^^^^
这就是高亮
3. 错误信息变得更加智能
,不再只是无情的才裁判,只会返回SyntaxError: invalid syntax
,更像是一位循循善诱的老师
来看看当我们写错时,老师
(Pyhton 3.10) 是怎么引导我们的
>>> # 条件语句忘记加冒号
>>> if rocket.position > event_horizon
File "<stdin>", line 1
if rocket.position > event_horizon
^
SyntaxError: expected ':'
>>> # 解包元组时没写括号
>>> {x,y for x,y in zip('abcd', '1234')}
File "<stdin>", line 1
{x,y for x,y in zip('abcd', '1234')}
^
SyntaxError: did you forget parentheses around the comprehension target?
>>> # 构造字典时,两个元素之间没加逗号
>>> items = {
... x: 1,
... y: 2
... z: 3,
File "<stdin>", line 3
y: 2
^
SyntaxError: invalid syntax. Perhaps you forgot a comma?
>>> # 准备补货多个异常,却少写了括号
>>> try:
... build_dyson_sphere()
... except NotEnoughScienceError, NotEnoughResourcesError:
File "<stdin>", line 3
except NotEnoughScienceError, NotEnoughResourcesError:
^
SyntaxError: multiple exception types must be parenthesized
缩进错误 IndentationErrors
现在缩进错误
会有更多关于期望缩进的块类型的上下文信息,包括语句的位置:
>>> def foo():
... if lel:
... x = 2
File "<stdin>", line 3
x = 2
^
IndentationError: expected an indented block after 'if' statement in line 2
属性错误 AttributeErrors
当出现熟悉错误
时,PyErr_Display
函数会猜你喜欢,打印出你可能要的属性:
>>> collections.namedtoplo
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: module 'collections' has no attribute 'namedtoplo'. Did you mean: namedtuple?
命名错误 NameErrors
和属性错误一样,当出现命名错误
时,PyErr_Display
函数会猜你喜欢,打印出你可能要的变量名:
>>> schwarzschild_black_hole = None
>>> schwarschild_black_hole
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
NameError: name 'schwarschild_black_hole' is not defined. Did you mean: schwarzschild_black_hole?
PyErr_Display
真是一个懂事的函数
switch-casematch-case终于来了
别人(Java、Golang、C)有的,你(Pyhton)也会有的,而且只会更好!
响应全网呼声,Python 版switch-case
,即match-case
也终于来了,这个特性也是 Python 3.10 中最受瞩目的特性
语法
Python 版的switch-case
,你要按照这个格式去写:
match subject:
case <pattern_1>:
<action_1>
case <pattern_2>:
<action_2>
case <pattern_3>:
<action_3>
case _:
<action_wildcard>
简单匹配
在没有match-case
之前,我们是这样写的:
def http_error_if_else(status):
if status == 400:
return "Bad request"
elif status == 404:
return "Not found"
elif status == 418:
return "I'm a teapot"
else:
return "Something's wrong with the internet"
# 或者这样
def http_error_dict(status):
http_status_to_error = {
400: "Bad request",
404: "Not found",
418: "I'm a teapot"
}
return http_status_to_error.get(status, "Something's wrong with the internet")
虽然可以解决问题,但我们知道if-else
在性能上和易读性上都没有switch-case
好用
再看看 Python 3.10 里,我们就可以这样写了:
def http_error_match_case(status):
match status:
case 400:
return "Bad request"
case 404:
return "Not found"
case 418:
return "I'm a teapot"
case _:
return "Something's wrong with the internet"
这就变得简单了许多
你还可以在case
后面用使用|
来串联多个,像这样:
case 401 | 403 | 404:
return "Not allowed"
如果不在case
语句中使用_
兜底,则可能不存在匹配项。如果不存在匹配项,则行为为空操作。例如,如果状态500
被传递,则会发生空操作。
同时匹配变量和常量
在进行匹配时,会按照case
后的pattern
对subject
尝试进行转换,来绑定pattern
中的变量,.在这个例子中,一个数据点可以解包到它的 x 坐标和 y 坐标:
# point is an (x, y) tuple
match point:
case (0, 0):
print("Origin")
case (0, y):
print(f"Y={y}")
case (x, 0):
print(f"X={x}")
case (x, y):
print(f"X={x}, Y={y}")
case _:
raise ValueError("Not a point")