The falsy values ??in Python include: empty string ''; numbers 0 and 0.0; empty list[]; empty dictionary {}; empty tuple(); boolean value False; special value None. Almost all other values ??except these values ??are truthy, such as non-zero numbers, non-empty strings, non-empty data structures, and default custom objects. In actual development, you need to pay attention to: if x is not None should be used; when processing function returns a value, you need to combine business logic to judge; the truthy/falsy feature can be used to simplify conditional expressions, but be careful to avoid misunderstandings or errors. Understanding the concepts of truthy and falsy helps to write more reliable and concise conditional judgment code.
In Python, many values ??are not Boolean types (True or False), but are treated as Boolean values ??in conditional judgments. This leads to the concepts of "truthy" and "falsy": simply put, the value that can be interpreted as True is truthy, which will be treated as True; otherwise, it is false, which will be treated as False.

This is very common when writing if statements, loop judgments or logical operations. Understanding them clearly can avoid some unexpected bugs.
What values ??are false?
There is a clear set of values ??in Python that will be processed as False
by default, which is the so-called falsy value . They include:

- Empty string
''
- Numbers
0
and0.0
- Empty list
[]
- Empty dictionary
{}
- Empty tuple
()
- Boolean value
False
- Special value
None
For example:
if '': print("This won't print")
This code will not output anything because the empty string is false and the conditional judgment fails.

All other values ??are basically truthy
Almost all other values ??except those falsy values ??listed above will be considered truthy even if they are not True
of Boolean type.
for example:
- Non-zero numbers:
1
,-5
,3.14
are all truthy - Non-empty string:
'hello'
,' '
(note that there are spaces) - Non-empty lists, dictionaries, collections, etc.: As long as it is not empty, it is truthy
- Custom objects, which are also truthy by default (unless you rewrite
__bool__
or__len__
methods)
So a judgment like the following will hold:
if [1, 2]: print("List is not empty") # This line will execute
Things to pay attention to in actual development
This implicit conversion is convenient when actually writing code, but it is also easy to cause misunderstandings or errors. There are several common usage scenarios that need attention:
Do not just use
if x:
when checking whether it is None , because 0 or an empty string will also be considered "not existed". A safer way is:if x is not None: ...
Function return value judgment : If you call a function, it may return 0 or an empty string. Although these are false, they do not mean that there is an error. You need to judge whether to deal with it based on the specific business logic.
Simplify conditional expressions : Sometimes we use the truthy/falsy feature to simplify the code, such as this:
name = input("Enter your name: ") or "Guest"
If the user input is empty, name will be set to "Guest".
Basically that's it. Understand which values ??are false and which are truthy, and you can avoid pitfalls when writing conditional judgments. Although it doesn't seem complicated, it's easy to ignore details, especially when dealing with data structures and function return values.
The above is the detailed content of python truthy and falsy values. For more information, please follow other related articles on the PHP Chinese website!

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