CODEWITHSUNDEEP
pythonpython-3.x
user17378
user17378

Reputation: 131

Why does the any() function return False?

I'm having difficulty using the all() and any() functions.

I have the following code below where I check for two adjacent digits are the same. Though the output of the print statements is not what I expect.

From my understanding:

any will return True if any of the values are True, while
the all will only return True if all of the values are True

Writing and running the code using Repl.it

test = 223456
number = str(test)
a = zip(number,number[1:])

#Checks for adjacent
equals = map(lambda x: x[0] == x[1], a)

print(list(equals))    #OUTPUT: [True, False, False, False, False]
print(any(equals))     #OUTPUT: False
print(all(equals))     #OUTPUT: True

Upvotes: 1

Views: 172

Answers (2)

r.ook
r.ook

Reputation: 13888

As the other answer covered, the main reason is that your map was already consumed prior to the any() and all() function. If you don't want to create a list to store the data (e.g. if there's a large amount of data), you could do a parallel operation instead:

>>> print(any(equals), all(equals), sep='\n')
True
False

Or if you need to do something with those values:

>>> a, b = any(equals), all(equals)
>>> a
True
>>> b
False

Just to make it clear, both zip and map are both generators that get consumed once iterated.

Upvotes: 0

C.Nivs
C.Nivs

Reputation: 13106

You have already consumed equals on the first call to list, since map is like a generator:

x = map(bool, range(1, 5))
print(list(x))
[True, True, True, True]
print(list(x))
[]

What you should do is convert it to a list or some data structure that allows you to iterate over it twice:

equals = list(map(lambda x: x[0] == x[1], a))

print(any(equals)) # True
print(all(equals)) # False

Where all will return True on an empty collection:

all([])
True

Upvotes: 6

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