chars-counter 0.4.0

Chars counter console util

chars-counter

A Python utility that counts, per ASCII category, how many characters appear exactly once in a given string. Works as both a CLI tool and an importable library.

Requires Python ≥ 3.14

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Installation

pip install chars-counter

uv add chars-counter

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CLI usage

Run the module directly with python -m chars_counter.

Count characters in a string

python -m chars_counter --string "Hello"
# Counter({<ASCIICharCategories.Lowercase_Letters: 'lowercase_letters'>: 2, <ASCIICharCategories.Uppercase_Letters: 'uppercase_letters'>: 1})

H appears once → 1 uppercase. e and o each appear once → 2 lowercase. l appears twice → ignored.

Count characters from a file

python -m chars_counter --file path/to/file.txt

Help

python -m chars_counter --help

Typo suggestions

Mistyped flags are caught and the closest valid flag is suggested:

python -m chars_counter --flie notes.txt
# --flie cannot be used, maybe you meant: --file

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Library usage

Basic example

from chars_counter import get_once_seen_chars_categories_count, ASCIICharCategories

result = get_once_seen_chars_categories_count("Hello")
# Counter({<ASCIICharCategories.Lowercase_Letters: 'lowercase_letters'>: 2,
#          <ASCIICharCategories.Uppercase_Letters: 'uppercase_letters'>: 1})

result[ASCIICharCategories.Lowercase_Letters]  # 2
result[ASCIICharCategories.Uppercase_Letters]  # 1

Iterating over results

from chars_counter import get_once_seen_chars_categories_count

result = get_once_seen_chars_categories_count("aA1")

for category, count in result.items():
    print(f"{category}: {count}")
# lowercase_letters: 1
# uppercase_letters: 1
# digits: 1

Empty / all-duplicate strings

Strings where every character appears more than once return an empty dict:

get_once_seen_chars_categories_count("aabb")  # Counter()
get_once_seen_chars_categories_count("")      # Counter()

Handling non-ASCII input

Passing a string that contains non-ASCII characters raises NotAsciiCharacterProvidedError:

from chars_counter import get_once_seen_chars_categories_count
from chars_counter.not_ascii_character_provided_error import NotAsciiCharacterProvidedError

try:
    get_once_seen_chars_categories_count("café")
except NotAsciiCharacterProvidedError as e:
    print(e.char)      # 'é'
    print(e.position)  # 3
    print(e)           # Non-ASCII character 'é' found at position 3.

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ASCII character categories

Category	Code points	Examples
Control_Characters	0–31, 127	\t, \n
Space	32
Punctuation	33–47, 58–64, 91–96, 123–126	!, ., @
Digits	48–57	0–9
Uppercase_Letters	65–90	A–Z
Lowercase_Letters	97–122	a–z

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Public API reference

get_once_seen_chars_categories_count(string: str) -> dict[ASCIICharCategories, int]

Returns a Counter mapping each ASCIICharCategories member to the number of characters in that category that appear exactly once in string. Categories with no once-seen characters are omitted.

Results are cached (lru_cache, capacity 1000).

Raises NotAsciiCharacterProvidedError if string contains any non-ASCII character.

ASCIICharCategories

A StrEnum with members: Control_Characters, Space, Punctuation, Digits, Uppercase_Letters, Lowercase_Letters.

Each member's string value is its snake_case name (e.g. ASCIICharCategories.Lowercase_Letters == "lowercase_letters").

NotAsciiCharacterProvidedError

Inherits from Exception. Attributes:

• char: str — the offending character
• position: int — its index in the input string

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Development

uv sync
uv run pytest
uv run coverage run -m pytest && uv run coverage report
uv run ruff format 
uv run ruff check --fix
uv run pyright