tsdat.tstring

Classes

Template

Python f-string implementation with lazy and optional variable substitutions.

class tsdat.tstring.Template(template: str, regex: str | None = None)

Python f-string implementation with lazy and optional variable substitutions.

The template string is expected to be formatted in the same way as python f-strings, with variables that should be substituted wrapped in curly braces {}. Additionally, square brackets may be used around curly brackets and other text to mark that substitution as optional – i.e. if the variable cannot be found then the text wrapped in the square brackets will be removed.

Examples

mapping = dict(a=”x”, b=”y”, c=”z”)

TemplateString(“{a}.{b}{c}w”).substitute(mapping) # -> “x.yzw”

TemplateString(“{a}.{b}[.{c}]”).substitute(mapping) # -> “x.y.z”

TemplateString(“{a}.{b}.{d}”).substitute(mapping) # raises ValueError

TemplateString(“{a}.{b}[.{d}]”).substitute(mapping) # -> “x.y”

TemplateString(“{a}.{b}.{d}”).substitute(mapping, True) # -> “x.y.{d}”

Parameters:

• template (str) – The template string. Variables to substitute should be wrapped by curly braces {}.

• regex (str | None, optional) – A regex pattern used to extract the substitutions used to create a formatted string with this template. Generated automatically if not provided.

Class Methods

__repr__	Return repr(self).
__str__	Return str(self).
extract_substitutions	Extracts the substitutions used to create the provided formatted string.
substitute	Substitutes variables in a template string.

Method Descriptions

__repr__() → str

Return repr(self).

__str__() → str

Return str(self).

extract_substitutions(formatted_str: str) → dict[str, str] | None

Extracts the substitutions used to create the provided formatted string.

Note that this is not guaranteed to return accurate results if the template is constructed such that separators between variables are ambiguous.

Parameters:

formatted_str (str) – The formatted string

Returns:

dict[str, str] –

A dictionary mapping each matched template variable to its

value in the formatted string. Returns None if there are no matches.

substitute(mapping: Mapping[str, str | Callable[[], str] | None] | None = None, allow_missing: bool = False, **kwds: str | Callable[[], str] | None) → str

Substitutes variables in a template string.

Parameters:

• mapping (Mapping[str, str | Callable[[], str] | None] | None) – A key-value pair of variable name to the value to replace it with. If the value is a string it is dropped-in directly. If it is a no-argument callable the return value of the callable is used. If it is None, then it is treated as missing and the action taken depends on the allow_missing parameter.

• allow_missing (bool, optional) – Allow variables outside of square brackets to be missing, in which case they are left as-is, including the curly brackets. This is intended to allow users to perform some variable substitutions before all variables in the mapping are known. Defaults to False.

• **kwds (str | Callable[[], str] | None) – Optional extras to be merged into the mapping dict. If a keyword passed here has the same name as a key in the mapping dict, the value here would be used instead.

Raises:

ValueError – If the substitutions cannot be made due to missing variables.

Returns:

str – The template string with the appropriate substitutions made.