12.1.1 The Formatter Interface
Interfaces to create formatters are dependent on the specific
formatter class being instantiated. The interfaces described below
are the required interfaces which all formatters must support once
One data element is defined at the module level:
Value which can be used in the font specification passed to the
push_font() method described below, or as the new value to any
push_property() method. Pushing the
value allows the corresponding
pop_property() method to
be called without having to track whether the property was changed.
The following attributes are defined for formatter instance objects:
The writer instance with which the formatter interacts.
- end_paragraph (blanklines)
Close any open paragraphs and insert at least blanklines
before the next paragraph.
- add_line_break ()
Add a hard line break if one does not already exist. This does not
break the logical paragraph.
- add_hor_rule (*args, **kw)
Insert a horizontal rule in the output. A hard break is inserted if
there is data in the current paragraph, but the logical paragraph is
not broken. The arguments and keywords are passed on to the writer's
- add_flowing_data (data)
Provide data which should be formatted with collapsed whitespace.
Whitespace from preceding and successive calls to
add_flowing_data() is considered as well when the whitespace
collapse is performed. The data which is passed to this method is
expected to be word-wrapped by the output device. Note that any
word-wrapping still must be performed by the writer object due to the
need to rely on device and font information.
- add_literal_data (data)
Provide data which should be passed to the writer unchanged.
Whitespace, including newline and tab characters, are considered legal
in the value of data.
- add_label_data (format, counter)
Insert a label which should be placed to the left of the current left
margin. This should be used for constructing bulleted or numbered
lists. If the format value is a string, it is interpreted as a
format specification for counter, which should be an integer.
The result of this formatting becomes the value of the label; if
format is not a string it is used as the label value directly.
The label value is passed as the only argument to the writer's
send_label_data() method. Interpretation of non-string label
values is dependent on the associated writer.
Format specifications are strings which, in combination with a counter
value, are used to compute label values. Each character in the format
string is copied to the label value, with some characters recognized
to indicate a transform on the counter value. Specifically, the
character "1" represents the counter value formatter as an
Arabic number, the characters "A" and "a"
represent alphabetic representations of the counter value in upper and
lower case, respectively, and "I" and "i"
represent the counter value in Roman numerals, in upper and lower
case. Note that the alphabetic and roman transforms require that the
counter value be greater than zero.
- flush_softspace ()
Send any pending whitespace buffered from a previous call to
add_flowing_data() to the associated writer object. This
should be called before any direct manipulation of the writer object.
- push_alignment (align)
Push a new alignment setting onto the alignment stack. This may be
AS_IS if no change is desired. If the alignment value is
changed from the previous setting, the writer's new_alignment()
method is called with the align value.
- pop_alignment ()
Restore the previous alignment.
- push_font (
(size, italic, bold, teletype
Change some or all font properties of the writer object. Properties
which are not set to AS_IS are set to the values passed in
while others are maintained at their current settings. The writer's
new_font() method is called with the fully resolved font
- pop_font ()
Restore the previous font.
- push_margin (margin)
Increase the number of left margin indentations by one, associating
the logical tag margin with the new indentation. The initial
margin level is
0. Changed values of the logical tag must be
true values; false values other than AS_IS are not
sufficient to change the margin.
- pop_margin ()
Restore the previous margin.
- push_style (*styles)
Push any number of arbitrary style specifications. All styles are
pushed onto the styles stack in order. A tuple representing the
entire stack, including AS_IS values, is passed to the
writer's new_styles() method.
- pop_style ([n
Pop the last n style specifications passed to
push_style(). A tuple representing the revised stack,
including AS_IS values, is passed to the writer's
- set_spacing (spacing)
Set the spacing style for the writer.
- assert_line_data ([flag
Inform the formatter that data has been added to the current paragraph
out-of-band. This should be used when the writer has been manipulated
directly. The optional flag argument can be set to false if
the writer manipulations produced a hard line break at the end of the
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