关于真实价值的问题 [英] question about True values

问题描述

我有点困惑。为什么在第一部分没有评价为True，

但它在第二部分呢？第一个陈述是不同的吗？

>> s =''hello''
s == True

False

>> if s：

print''hi ''

hi

>>>

谢谢。

解决方案

John Salerno< ; jo ****** @ NOSPAMgmail.com写：

我有点困惑。为什么在第一个

部分中没有评价为True，但是它在第二部分呢？第一个声明是什么

不同？

编号True和False是布尔值，其中布尔值是来自字符串的不同的数据类型，就像字符串与整数不同。

>> if s：

print''hi''

在评估期间将s转换为布尔值。也就是说，它与


相同如果bool（s）：print''hi''


bool（s）是一个将s转换为bool的函数。如果s是一个字符串，

bool（s）如果s是非空的则为true，否则为false。


与整数相似的东西：假设


x = 3.1


然后x == 3是假的，但是int（x）== 3是的。

John我有点困惑。为什么在第一个

Johnpart中没有评价为True，但它在第二个时间是否存在？第一个陈述是什么

Johndifferent？

>> ; s =''你好''
s == True

False

>> if s：

...打印''hi''

hi


s不等于布尔对象True，但它也不是评估为

字符串类''nil"值。每个内置类型都有这样一个空白的bb空。或nil或nil值：


string"

list []

元组（）

dict {}

int 0

float 0.0

complex 0j

set set（）


除上述之外的任何其他值将比较为非假。


跳过

John Salerno写道：

我有点困惑。为什么在第一部分没有评价为True，

但它在第二部分呢？第一个陈述是不同的吗？

>> s =''hello''

>> s == True

False

>> if s：

print''hi''


hi

>>>

谢谢。

优秀的问题！这应该有所帮助：

>> s =" Hello"
s

''Hello''

>> bool（s）

True
< blockquote class =post_quotes>

>> s == True

False


s的值不等于True的值。但是，s的* boolean *

值为True，因为它不是0或空字符串。 python

''if''语句计算条件表达式的布尔值。

I''m a little confused. Why doesn''t s evaluate to True in the first part,
but it does in the second? Is the first statement something different?

>>s = ''hello''
s == True

False

>>if s:

print ''hi''
hi

>>>

Thanks.

解决方案

John Salerno <jo******@NOSPAMgmail.comwrites:

I''m a little confused. Why doesn''t s evaluate to True in the first
part, but it does in the second? Is the first statement something
different?

No. True and False are boolean values, where booleans are a different
data type from strings, just like strings are different from integers.

>>if s:

print ''hi''

converts s to a boolean during evaluation. That is, it''s the same as

if bool(s): print ''hi''

bool(s) is a function that converts s to a bool. If s is a string,
bool(s) is true if s is nonempty, false otherwise.

A comparable thing with integers: suppose

x = 3.1

then "x == 3" is false, but "int(x) == 3" is true.

JohnI''m a little confused. Why doesn''t s evaluate to True in the first
Johnpart, but it does in the second? Is the first statement something
Johndifferent?

>>s = ''hello''
s == True

False

>>if s:

... print ''hi''
hi

s is not equal to the boolean object True, but it also doesn''t evaluate to
the string class''s "nil" value. Each of the builtin types has such an
"empty" or "nil" value:

string ""
list []
tuple ()
dict {}
int 0
float 0.0
complex 0j
set set()

Any other value besides the above will compare as "not false".

Skip

John Salerno wrote:

I''m a little confused. Why doesn''t s evaluate to True in the first part,
but it does in the second? Is the first statement something different?

>>s = ''hello''
>>s == True

False

>>if s:

print ''hi''
hi

>>>

Thanks.

Excellent question! This should help:

>>s = "Hello"
s

''Hello''

>>bool(s)

True

>>s == True

False

The value of s is not equal to the value of True. But, the *boolean*
value of s is True, since it is not 0 or an empty string. The python
''if'' statement evaluates the boolean value of the condition expression.

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