Filter a list containing specific string-CodePudding

My Goal

I have a specific set of a long list containing many asset pairs with different endings: BTCUSDT ETHBTC ANKRETH... From this list, I would like to filter out the symbols ending with USDT.

My Problem:

I have tried using filter and all with iterations, however, none provides the exact result.

Here are my attempts:

Attempt 1:

my_set = ['LUNAUSDT', 'ETHBTC', 'ETHBNB', 'BTCUSDT', 'MANATUSD', 'ALICEETH' ]
my_set = [word for word in symbols if 'USDT' in my_set]
my_set

This results in an empty set.

Attempt 2:

keyword = ['USDT']
my_set = ['LUNAUSDT', 'ETHBTC', 'ETHBNB', 'BTCUSDT', 'MANATUSD', 'ALICEETH' ]
final = [ x for x in my_set in all(keyword in keyword for keyword in my_set)]
final

This results in the error:

TypeError: argument of type 'bool' is not iterable

Attempt 3:

my_final_set = filter(lambda x:x.endswith(("USDT")), my_set)
my_final_set

This shows: <filter at 0x7fe537eebf10>

I basically want my final list with all symbols ending with USDT

For example:

my_set = ['LUNAUSDT', 'ETHBTC', 'ETHBNB', 'BTCUSDT', 'MANATUSD', 'ALICEETH' ]

results in: ['LUNAUSDT', 'BTCUSDT']

Any help or advice on what I'm doing wrong would be massively appreciated. Thanks in advance!

CodePudding user response：

You're almost there. Try this:

my_set = ['LUNAUSDT', 'ETHBTC', 'ETHBNB', 'BTCUSDT', 'MANATUSD', 'ALICEETH' ]
final = [word for word in my_set if 'USDT' in word]
print(final)

For your Attempt 3, make this change:

my_final_set = list(filter(lambda x:x.endswith(("USDT")), my_set))

One another method is to use .endswith():

final = [word for word in my_set if word.endswith('USDT')]
print(final)

Output:

['LUNAUSDT', 'BTCUSDT']

CodePudding user response：

solution using filter function and list-comprehension

my_set = ['LUNAUSDT', 'ETHBTC', 'ETHBNB', 'BTCUSDT', 'MANATUSD', 'ALICEETH' ]
keyword = 'USDT'

result1 = list(filter(lambda word: word.endswith(keyword), my_set))
result2 = [ word for word in my_set if word.endswith(keyword)]

CodePudding user response：

You can use regex:

import re

my_set = ['LUNAUSDT', 'ETHBTC', 'ETHBNB', 'BTCUSDT', 'MANATUSD', 'ALICEETH' ]

my_filtered_set = [ i for i in my_set if re.search('USD$',i) ]

CodePudding user response：

Attempt 1

[word for word in symbols if 'USDT' in my_set]

This has two mistakes:

'USDT' in my_set checks if 'USDT' is contained in the input list, not if it is contained in one of the words from the input list. You should have used 'USDT' in word.
'USDT' in word would check if 'USDT' is contained anywhere in word (not just at the end). In order to check if a string ends with a particular suffix, use word.endswith('USDT').

Attempt 2

[ x for x in my_set in all(keyword in keyword for keyword in my_set)]

This makes the least sense of your attempts. all(...) returns either True or False, depending on whether a condition is true for all elements from an iterable. In this case keyword in keyword is obviously true for all words keyword from my_set, so this would be equivalent to

[x for x in my_set in True]

Here, Python would try to evaluate my_set in True as if True were some sort of collection. It attempts this by trying to iterate over True (and then checking in turn if any item is equal to my_set), which is not possible.

Attempt 3

filter(lambda x:x.endswith(("USDT")), my_set)

This is mostly correct, however filter returns an iterator, which only returns the results as you iterate over it. In order to get a list, you have to consume the iterator:

list(filter(lambda x: x.endswith(("USDT")), my_set))

which is approximately equivalent to

result = []
for y in filter(lambda x: x.endswith(("USDT")), my_set):
    result.append(y)

See Why does foo = filter(...) return a <filter object>, not a list?