Pythonformatter通用格式化输出

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 initialized.

One data element is defined at the module level:

formatter.AS_IS¶

Value which can be used in the font specification passed to the push_font()

method described below, or as the new value to any other push_property()

method. Pushing the AS_IS 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:

formatter.writer¶

The writer instance with which the formatter interacts.

formatter.end_paragraph(blanklines)¶

Close any open paragraphs and insert at least blanklines before the next

paragraph.

formatter.add_line_break()¶

Add a hard line break if one does not already exist. This does not break the

logical paragraph.

formatter.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 send_line_break()

method.

formatter.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.

formatter.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.

formatter.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.

formatter.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.

formatter.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.

formatter.pop_alignment()¶

Restore the previous alignment.

formatter.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 specification.

formatter.pop_font()¶

Restore the previous font.

formatter.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.

formatter.pop_margin()¶

Restore the previous margin.

formatter.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.

formatter.pop_style(n=1)¶

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 new_styles() method.

formatter.set_spacing(spacing)¶

Set the spacing style for the writer.

formatter.assert_line_data(flag=1)¶

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 output.

Formatter Implementations¶

Two implementations of formatter objects are provided by this module. Most

applications may use one of these classes without modification or subclassing.

class formatter.NullFormatter(writer=None)¶

A formatter which does nothing. If writer is omitted, a NullWriter

instance is created. No methods of the writer are called by

NullFormatter instances. Implementations should inherit from this

class if implementing a writer interface but don't need to inherit any

implementation.

class formatter.AbstractFormatter(writer)¶

The standard formatter. This implementation has demonstrated wide applicability

to many writers, and may be used directly in most circumstances. It has been

used to implement a full-featured World Wide Web browser.

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.

writer.flush()¶

Flush any buffered output or device control events.

writer.new_alignment(align)¶

Set the alignment style. The align value can be any object, but by convention

is a string or None, where None indicates that the writer's "preferred"

alignment should be used. Conventional align values are 'left',

'center', 'right', and 'justify'.

writer.new_font(font)¶

Set the font style. The value of font will be None, indicating that the

device's default font should be used, or a tuple of the form (size,

italic,bold,teletype). 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.

writer.new_margin(margin, level)¶

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 level.

writer.new_spacing(spacing)¶

Set the spacing style to spacing.

writer.new_styles(styles)¶

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 implementation.

writer.send_line_break()¶

Break the current line.

writer.send_paragraph(blankline)¶

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.

writer.send_hor_rule(*args, **kw)¶

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().

writer.send_flowing_data(data)¶

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.

writer.send_literal_data(data)¶

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 send_formatted_data() interface.

writer.send_label_data(data)¶

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.

Writer Implementations¶

Three implementations of the writer object interface are provided as examples by

this module. Most applications will need to derive new writer classes from the

NullWriter class.

class formatter.NullWriter¶

A writer which only provides the interface definition; no actions are taken on

any methods. This should be the base class for all writers which do not need to

inherit any implementation methods.

class formatter.AbstractWriter¶

A writer which can be used in debugging formatters, but not much else. Each

method simply announces itself by printing its name and arguments on standard

output.

class formatter.DumbWriter(file=None, maxcol=72)¶

Simple writer class which writes output on the file object passed

in as file or, if file is omitted, on standard output. The output is

simply word-wrapped to the number of columns specified by maxcol. This

class is suitable for reflowing a sequence of paragraphs.