pyforma 0.3.0

A python template engine

PyForma

A Python template engine featuring partial substitution.

Example

from pyforma import Template

template = Template("Hello, {{ subject }}! This is {{ lib_name }}.")
assert template.unresolved_identifiers() == {"subject", "lib_name"}

template = template.substitute({"lib_name": "PyForma"})
assert template.unresolved_identifiers() == {"subject"}

print(template.render({"subject": "World"}))  # Prints "Hello, World! This is PyForma."

Features

• 100% Python
• Python-like expressions in templates
• Special-purpose environments for more expressive templates
• Templates can be inspected for what variables need to be substituted
• Can partially substitute variables within templates
• Rendering with undefined variables results in an error
• Fully statically typed

API

pyforma.Template(content, /, *, syntax)

The primary template class.

Parameters:

• content: str | Path:
  If str, parses the string as a template.
  If Path, reads the file at that path and parses it as a template.
• syntax: TemplateSyntaxConfig | None :
  Optional syntax definition.

Return Value:

Returns the template object.

Exceptions:

• ValueError: The provided input is not a valid template.
• OSError: If a path is passed and the file cannot be opened

pyforma.Template.unresolved_identifiers() -> set[str]

Reports all identifiers that need to be substituted to render the template.

Return Value:

Returns the set of all remaining identifiers in the template.

pyforma.Template.substitute(variables, *, keep_comments, renderers) -> Template

Partially substitutes variables in the template and evaluates expressions that can be evaluated.

Parameters:

• variables: dict[str, Any]:
  Dictionary mapping variable identifiers to their values.
• keep_comments: bool:
  By default, comments are kept until the final rendering. Set to False to strip all comments.
• renderers: Sequence[tuple[type, Callable[[Any], str]]] | None:
  Optional sequence of renderers for stringification. By default, only str, int and float are rendered to str during template substitution. This argument can be used to automatically render additional types. Alternatively, the template needs to explicitly format other types as str.

Return Value:

A new template identical to self, but with the provided variables substituted.

Exceptions:

• ValueError: An expression evaluates to a type that can not be rendered.

pyforma.Template.render(variables, *, renderers) -> str

Renders a template to a string.

Parameters:

• variables: dict[str, Any] | None:
  Optional dictionary mapping variable identifiers to their values.
• renderers: Sequence[tuple[type, Callable[[Any], str]]] | None:
  Optional sequence of renderers for stringification. See substitute() for details.

Return Value:

The rendered string with all variables substituted.

Exceptions:

• ValueError:
  • Some unresolved variables remain after substitution.
  • An expression evaluates to a type that can not be rendered.

pyforma.TemplateSyntaxConfig(comment, expression, environment)

Template syntax configuration class.

Parameters:

• comment: BlockSyntaxConfig:
  Configuration for comment blocks. Defaults to BlockSyntaxConfig("{#", "#}").
• expression: BlockSyntaxConfig:
  Configuration for expression blocks. Defaults to BlockSyntaxConfig("{{", "}}").
• environment: BlockSyntaxConfig:
  Configuration for environment blocks. Defaults to BlockSyntaxConfig("{%", "%}").

Exceptions:

• ValueError: The configured symbols are not sufficiently distinct.

pyforma.BlockSyntaxConfig(open, close)

Class used for configuring the syntax of a block type.

Parameters:

• open: str:
  Open block syntax. Must not be empty.
• close: str:
  Close block syntax. Must not be empty.

Exceptions:

• ValueError:
  • Either of the parameters is empty.
  • The provided parameters are identical.

Alternatives

• Jinja2: The de-facto standard Python template engine. It's popular, fast, expressive and extensible, but doesn't support partial template substitution.
• Mako: Compiles templates to Python bytecode.
• Chameleon: HTML/XML-compatible template engine.
• string.Template: The actual standard Python template engine. Pretty limited functionality.