Why "[ ] and {}" expression return [ ] in python?(Why are [] and {} false?) [duplicate]

Question

I am wondering about why [] and {} return [] in python?

>>> [] and {}
[]

Edit: Why are [] and {} false?I understand and or expressions , but i cannot understand [] and {} expressions are false?

Why [] and {} false?I understand and or expressions , but i cannot understand [] and {} expressions are false? — my-lord
– my-lord, Commented Feb 25, 2018 at 21:02
@mw-b, ...because they're empty. See ie. empty list boolean value, or How do I check if a list is empty?. — Charles Duffy
– Charles Duffy, Commented Feb 25, 2018 at 21:09

heemayl · Accepted Answer · 2018-02-25 20:46:31Z

3

In the short circuit evaluation containing only operator and (could be multiple) and multiple operators, the expression returns the first falsy value, in this case which is [] -- an empty list.

In the case where all the values are truthy, it returns the last value.

# [] and {} both are falsey
In [77]: [] and {}
Out[77]: []

# 3 is truthy, {} is falsey
In [78]: 3 and {}
Out[78]: {}

# all except {} are truthy
In [79]: 3 and 9 and {}
Out[79]: {}

# you get it...
In [80]: 3 and 9 and {} and 10
Out[80]: {}

edited Feb 25, 2018 at 20:46

answered Feb 25, 2018 at 20:42

heemayl

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3 Comments

Ziyad Edher Over a year ago

In addition to this, the reason that the first falsy value is returned rather than some other one like the last or middle is that of an optimization technique called short-circuit evaluation.

avigil Over a year ago

or the second value if neither are falsey

heemayl Over a year ago

@avigil Just added.

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