如何在Python中将字符串转换为布尔值?这个尝试返回True:
>>> bool("False")
True
如何在Python中将字符串转换为布尔值?这个尝试返回True:
>>> bool("False")
True
当前回答
这是我的版本。它同时检查正值和负值列表,对于未知值引发异常。它不接收字符串,但任何类型都可以。
def to_bool(value):
"""
Converts 'something' to boolean. Raises exception for invalid formats
Possible True values: 1, True, "1", "TRue", "yes", "y", "t"
Possible False values: 0, False, None, [], {}, "", "0", "faLse", "no", "n", "f", 0.0, ...
"""
if str(value).lower() in ("yes", "y", "true", "t", "1"): return True
if str(value).lower() in ("no", "n", "false", "f", "0", "0.0", "", "none", "[]", "{}"): return False
raise Exception('Invalid value for boolean conversion: ' + str(value))
示例:
>>> to_bool(True)
True
>>> to_bool("tRUe")
True
>>> to_bool("1")
True
>>> to_bool(1)
True
>>> to_bool(2)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 9, in to_bool
Exception: Invalid value for boolean conversion: 2
>>> to_bool([])
False
>>> to_bool({})
False
>>> to_bool(None)
False
>>> to_bool("Wasssaaaaa")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 9, in to_bool
Exception: Invalid value for boolean conversion: Wasssaaaaa
>>>
其他回答
从Python 2.6开始,你可以使用ast.literal_eval:
>>> import ast >>> help(ast.literal_eval) Help on function literal_eval in module ast: literal_eval(node_or_string) Safely evaluate an expression node or a string containing a Python expression. The string or node provided may only consist of the following Python literal structures: strings, numbers, tuples, lists, dicts, booleans, and None.
这似乎是可行的,只要你确定你的字符串将是“True”或“False”:
>>> ast.literal_eval("True") True >>> ast.literal_eval("False") False >>> ast.literal_eval("F") Traceback (most recent call last): File "", line 1, in File "/opt/Python-2.6.1/lib/python2.6/ast.py", line 68, in literal_eval return _convert(node_or_string) File "/opt/Python-2.6.1/lib/python2.6/ast.py", line 67, in _convert raise ValueError('malformed string') ValueError: malformed string >>> ast.literal_eval("'False'") 'False'
我通常不建议这样做,但它是完全内置的,可以根据您的需求来选择。
如果你知道你的输入将是“True”或其他什么,那么为什么不使用:
def bool_convert(s):
return s == "True"
我必须这么做……所以,也许姗姗来迟——但有人可能会发现它很有用
def str_to_bool(input, default):
"""
| Default | not_default_str | input | result
| T | "false" | "true" | T
| T | "false" | "false" | F
| F | "true" | "true" | T
| F | "true" | "false" | F
"""
if default:
not_default_str = "false"
else:
not_default_str = "true"
if input.lower() == not_default_str:
return not default
else:
return default
这是我的版本。它同时检查正值和负值列表,对于未知值引发异常。它不接收字符串,但任何类型都可以。
def to_bool(value):
"""
Converts 'something' to boolean. Raises exception for invalid formats
Possible True values: 1, True, "1", "TRue", "yes", "y", "t"
Possible False values: 0, False, None, [], {}, "", "0", "faLse", "no", "n", "f", 0.0, ...
"""
if str(value).lower() in ("yes", "y", "true", "t", "1"): return True
if str(value).lower() in ("no", "n", "false", "f", "0", "0.0", "", "none", "[]", "{}"): return False
raise Exception('Invalid value for boolean conversion: ' + str(value))
示例:
>>> to_bool(True)
True
>>> to_bool("tRUe")
True
>>> to_bool("1")
True
>>> to_bool(1)
True
>>> to_bool(2)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 9, in to_bool
Exception: Invalid value for boolean conversion: 2
>>> to_bool([])
False
>>> to_bool({})
False
>>> to_bool(None)
False
>>> to_bool("Wasssaaaaa")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 9, in to_bool
Exception: Invalid value for boolean conversion: Wasssaaaaa
>>>
dict(实际上是defaultdict)为你提供了一种非常简单的方法:
from collections import defaultdict
bool_mapping = defaultdict(bool) # Will give you False for non-found values
for val in ['True', 'yes', ...]:
bool_mapping[val] = True
print(bool_mapping['True']) # True
print(bool_mapping['kitten']) # False
将这个方法定制为您想要的确切转换行为非常容易——您可以用允许的Truthy和Falsy值填充它,并在没有找到值时让它引发异常(或返回None),或默认为True,或默认为False,或任何您想要的。