12.1.3 The Writer Interface
Interfaces to create writers are dependent on the specific writer
class being instantiated. The interfaces described below are the
required interfaces which all writers must support once initialized.
Note that while most applications can use the
AbstractFormatter class as a formatter, the writer must
typically be provided by the application.
Flush any buffered output or device control events.
Set the alignment style. The align value can be any object,
but by convention is a string or
indicates that the writer's ``preferred'' alignment should be used.
Conventional align values are
Set the font style. The value of font will be
indicating that the device's default font should be used, or a tuple
of the form
(size, italic, bold,
). Size will be a string indicating the size of
font that should be used; specific strings and their interpretation
must be defined by the application. The italic, bold, and
teletype values are Boolean values specifying which of those
font attributes should be used.
Set the margin level to the integer level and the logical tag
to margin. Interpretation of the logical tag is at the
writer's discretion; the only restriction on the value of the logical
tag is that it not be a false value for non-zero values of
Set the spacing style to spacing.
Set additional styles. The styles value is a tuple of
arbitrary values; the value AS_IS should be ignored. The
styles tuple may be interpreted either as a set or as a stack
depending on the requirements of the application and writer
Break the current line.
Produce a paragraph separation of at least blankline blank
lines, or the equivalent. The blankline value will be an
integer. Note that the implementation will receive a call to
send_line_break() before this call if a line break is needed;
this method should not include ending the last line of the paragraph.
It is only responsible for vertical spacing between paragraphs.
Display a horizontal rule on the output device. The arguments to this
method are entirely application- and writer-specific, and should be
interpreted with care. The method implementation may assume that a
line break has already been issued via send_line_break().
Output character data which may be word-wrapped and re-flowed as
needed. Within any sequence of calls to this method, the writer may
assume that spans of multiple whitespace characters have been
collapsed to single space characters.
Output character data which has already been formatted
for display. Generally, this should be interpreted to mean that line
breaks indicated by newline characters should be preserved and no new
line breaks should be introduced. The data may contain embedded
newline and tab characters, unlike data provided to the
Set data to the left of the current left margin, if possible.
The value of data is not restricted; treatment of non-string
values is entirely application- and writer-dependent. This method
will only be called at the beginning of a line.
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