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The parsers module provides utilities for parsing and validating user input into strongly-typed domain model objects. These functions are used by both the CLI and MCP interfaces to ensure consistent parameter handling.

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resolve_enum

Resolve an enum member by name with normalized errors. 
def resolve_enum(enum_cls: type[T], name: str) -> T
​
enum_cls
type[T]
required
The enum class to resolve from
​
name
str
required
The name of the enum member (case-insensitive)
Returns: The resolved enum member Raises: ParseError if the name is not a valid enum member

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Usage

from fli.core.parsers import resolve_enum
from fli.models import SeatType

seat_type = resolve_enum(SeatType, "economy")  # Returns SeatType.ECONOMY

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resolve_airport

Resolve an airport code to an Airport enum. 
def resolve_airport(code: str) -> Airport
​
code
str
required
IATA airport code (e.g., ‘JFK’, ‘LHR’)
Returns: The corresponding Airport enum member Raises: ParseError if the code is not a valid airport

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Usage

from fli.core.parsers import resolve_airport

origin = resolve_airport("JFK")  # Returns Airport.JFK
destination = resolve_airport("LHR")  # Returns Airport.LHR

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parse_airlines

Parse a list of airline codes into Airline enums. 
def parse_airlines(codes: list[str] | None) -> list[Airline] | None
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codes
list[str] | None
required
List of IATA airline codes (e.g., [‘BA’, ‘KL’]). Can be None.
Returns: List of Airline enums, or None if input is empty Raises: ParseError if any code is not a valid airline

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Usage

from fli.core.parsers import parse_airlines

airlines = parse_airlines(["DL", "UA"])  # Returns [Airline.DL, Airline.UA]
no_filter = parse_airlines(None)  # Returns None

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parse_max_stops

Parse a stops parameter into a MaxStops enum. Accepts both string names (ANY, NON_STOP, ONE_STOP, TWO_PLUS_STOPS) and integer values (0, 1, 2+). 
def parse_max_stops(stops: str) -> MaxStops
​
stops
str
required
Stops value as string or integer representation. Valid values:
  • String names: "ANY", "NON_STOP", "NONSTOP", "ONE_STOP", "ONE_STOP_OR_FEWER", "TWO_PLUS_STOPS", "TWO_OR_FEWER_STOPS"
  • Integers: "0" (non-stop), "1" (one stop or fewer), "2" (two or fewer stops)
Returns: The corresponding MaxStops enum member Raises: ParseError if the value is not valid

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Usage

from fli.core.parsers import parse_max_stops

# Using string names
max_stops = parse_max_stops("NON_STOP")  # Returns MaxStops.NON_STOP
max_stops = parse_max_stops("ONE_STOP")  # Returns MaxStops.ONE_STOP_OR_FEWER

# Using integer values
max_stops = parse_max_stops("0")  # Returns MaxStops.NON_STOP
max_stops = parse_max_stops("1")  # Returns MaxStops.ONE_STOP_OR_FEWER
max_stops = parse_max_stops("2")  # Returns MaxStops.TWO_OR_FEWER_STOPS

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parse_cabin_class

Parse a cabin class string into a SeatType enum. 
def parse_cabin_class(cabin_class: str) -> SeatType
​
cabin_class
str
required
Cabin class name. Valid values: "ECONOMY", "PREMIUM_ECONOMY", "BUSINESS", "FIRST"
Returns: The corresponding SeatType enum member Raises: ParseError if the value is not valid

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Usage

from fli.core.parsers import parse_cabin_class

cabin_class = parse_cabin_class("ECONOMY")  # Returns SeatType.ECONOMY
cabin_class = parse_cabin_class("BUSINESS")  # Returns SeatType.BUSINESS

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parse_sort_by

Parse a sort_by string into a SortBy enum. 
def parse_sort_by(sort_by: str) -> SortBy
​
sort_by
str
required
Sort option. Valid values: "CHEAPEST", "DURATION", "DEPARTURE_TIME", "ARRIVAL_TIME"
Returns: The corresponding SortBy enum member Raises: ParseError if the value is not valid

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Usage

from fli.core.parsers import parse_sort_by

sort_option = parse_sort_by("CHEAPEST")  # Returns SortBy.CHEAPEST
sort_option = parse_sort_by("DURATION")  # Returns SortBy.DURATION

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parse_time_range

Parse a time range string into start and end hours. 
def parse_time_range(time_range: str) -> tuple[int, int]
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time_range
str
required
Time range in ‘HH-HH’ format (e.g., ‘6-20’ for 6 AM to 8 PM)
Returns: Tuple of (start_hour, end_hour) where hours are integers from 0-23 Raises: ParseError if the format is invalid or hours are out of range

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Usage

from fli.core.parsers import parse_time_range

start, end = parse_time_range("6-20")  # Returns (6, 20)
start, end = parse_time_range("8-22")  # Returns (8, 22)

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ParseError

Exception raised when parsing fails. 
class ParseError(ValueError):
    """Error raised when parsing fails."""
All parser functions raise ParseError when they encounter invalid input. This exception inherits from ValueError and includes descriptive error messages with valid value suggestions.

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Usage

from fli.core.parsers import parse_cabin_class, ParseError

try:
    cabin_class = parse_cabin_class("INVALID")
except ParseError as e:
    print(e)  # "Invalid cabin_class value: 'INVALID'. Valid values: ECONOMY, PREMIUM_ECONOMY, BUSINESS, FIRST"

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Complete example

Here’s how the parser functions are used together in the MCP server: 
from fli.core.parsers import (
    resolve_airport,
    parse_airlines,
    parse_cabin_class,
    parse_max_stops,
    parse_sort_by,
)

# Parse all search parameters
origin = resolve_airport("JFK")
destination = resolve_airport("LHR")
cabin_class = parse_cabin_class("ECONOMY")
max_stops = parse_max_stops("NON_STOP")
sort_by = parse_sort_by("CHEAPEST")
airlines = parse_airlines(["BA", "DL"])

# These are now ready to use in FlightSearchFilters

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