杰瑞科技汇

Python为何说not true?逻辑值藏着什么?

That's an interesting statement! In Python, the keyword True is a boolean value that represents truth. So, the statement python is not true is comparing the string "python" to the boolean value True.

Let's break down what that comparison means.

The Short Answer

The expression "python" is not True evaluates to True.

A string is not the same thing as the boolean value True, so the statement is correct.


The Detailed Explanation

In Python, different data types are distinct. The string "python" and the boolean True belong to two different types:

  • "python" is of type str (string).
  • True is of type bool (boolean).

Because they are different objects of different types, they are not identical.

The is Operator

The is operator checks for object identity. It asks, "Are these two variables pointing to the exact same object in memory?" Since a string and a boolean are fundamentally different types of objects, they can never be the same object.

# Let's check their types
print(type("python"))  # Output: <class 'str'>
print(type(True))     # Output: <class 'bool'>
# The 'is' operator confirms they are different objects
print("python" is True)      # Output: False
print("python" is not True)  # Output: True

Truthiness and the Operator

This is where it gets more nuanced and is likely the source of the confusion. While "python" is not True is correct, people often wonder about its "truthiness."

In Python, many objects have an inherent truthiness. When used in a boolean context (like an if statement), they are evaluated as either True or False.

  • "Truthy" values are those that evaluate to True.
    • Most objects are considered truthy (e.g., non-empty strings like "python", non-zero numbers like 1, lists, dictionaries, etc.).
  • "Falsy" values are those that evaluate to False.
    • Examples include None, False, 0, 0, empty sequences (, [], ), and empty mappings ().

So, while the string "python" is not the same object as True, it is a truthy value.

if "python":
    print("The string 'python' is truthy!") # This line will be executed
if True:
    print("The boolean True is truthy!") # This line will also be executed

This is why you might see code like this, which is a common Python idiom:

my_variable = "some value"
# Check if my_variable is truthy (i.e., not None, not an empty string, etc.)
if my_variable:
    print("my_variable has a value.")
# This is generally preferred over:
if my_variable != None:
    print("my_variable is not None.")

Summary

Expression Result Why?
"python" is True False A string (str) is not the same object as a boolean (bool).
"python" is not True True Correctly identifies they are different types.
bool("python") True The string "python" is "truthy" because it's not empty.
if "python": The block is executed Because "python" is a truthy value.

So, your original statement, "python is not true," is correct in the literal sense of Python's is operator. However, it's important to understand that the string "python" is still considered a "truthy" value in boolean contexts.

分享:
扫描分享到社交APP
上一篇
下一篇