solution.py

# Write a function that takes a piece of text in the form of a string
# and returns the letter frequency count for the text.
# This count excludes numbers, spaces and all punctuation marks.
# Upper and lower case versions of a character are equivalent and the result should all be in lowercase.

# The function should return a list of tuples (in Python and Haskell) or arrays (in other languages)
# sorted by the most frequent letters first. The Rust implementation should return an ordered BTreeMap.
# Letters with the same frequency are ordered alphabetically. For example:

# letter_frequency('aaAabb dddDD hhcc')
# will return

# [('d',5), ('a',4), ('b',2), ('c',2), ('h',2)]
from collections import Counter


def letter_frequency(text):
    chars = Counter(c for c in text.lower() if c.isalpha())
    return sorted(chars.items(), key=lambda x: (-x[1], x[0]))