Fix lay-out glitches and remove gmail turd.
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Guido van Rossum
parent
564e85c33f
commit
9934e842de
129
pep-3138.txt
129
pep-3138.txt
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@ -29,20 +29,20 @@ algorithm.
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- Convert CR, LF, TAB and '\\' to '\\r', '\\n', '\\t', '\\\\'.
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- Convert other non-printable characters(0x00-0x1f, 0x7f) and non-ASCII
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characters(>=0x80) to '\\xXX'.
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characters(>=0x80) to '\\xXX'.
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- Backslash-escape quote characters (apostrophe, ') and add the quote
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character at the beginning and the end.
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character at the beginning and the end.
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For Unicode strings, the following additional conversions are done.
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- Convert leading surrogate pair characters without trailing character
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(0xd800-0xdbff, but not followed by 0xdc00-0xdfff) to '\\uXXXX'.
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(0xd800-0xdbff, but not followed by 0xdc00-0xdfff) to '\\uXXXX'.
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- Convert 16-bit characters(>=0x100) to '\\uXXXX'.
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- Convert 21-bit characters(>=0x10000) and surrogate pair characters to
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'\\U00xxxxxx'.
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'\\U00xxxxxx'.
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This algorithm converts any string to printable ASCII, and repr() is
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used as a handy and safe way to print strings for debugging or for
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@ -75,19 +75,19 @@ Specification
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=============
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- Add a new function to the Python C API ``int Py_UNICODE_ISPRINTABLE
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(Py_UNICODE ch)``. This function returns 0 if repr() should escape the
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Unicode character ``ch``; otherwise it returns 1. Characters that should
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be escaped are defined in the Unicode character database as:
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(Py_UNICODE ch)``. This function returns 0 if repr() should escape the
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Unicode character ``ch``; otherwise it returns 1. Characters that should
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be escaped are defined in the Unicode character database as:
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* Cc (Other, Control)
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* Cf (Other, Format)
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* Cs (Other, Surrogate)
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* Co (Other, Private Use)
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* Cn (Other, Not Assigned)
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* Zl (Separator, Line), refers to LINE SEPARATOR ('\\u2028').
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* Zp (Separator, Paragraph), refers to PARAGRAPH SEPARATOR ('\\u2029').
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* Zs (Separator, Space) other than ASCII space('\\x20'). Characters in
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this category should be escaped to avoid ambiguity.
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* Cc (Other, Control)
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* Cf (Other, Format)
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* Cs (Other, Surrogate)
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* Co (Other, Private Use)
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* Cn (Other, Not Assigned)
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* Zl (Separator, Line), refers to LINE SEPARATOR ('\\u2028').
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* Zp (Separator, Paragraph), refers to PARAGRAPH SEPARATOR ('\\u2029').
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* Zs (Separator, Space) other than ASCII space('\\x20'). Characters in
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this category should be escaped to avoid ambiguity.
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- The algorithm to build repr() strings should be changed to:
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@ -105,22 +105,22 @@ Specification
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character at the beginning and the end.
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- Set the Unicode error-handler for sys.stderr to 'backslashreplace' by
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default.
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default.
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- Add ``'%a'`` string format operator. ``'%a'`` converts any python
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object to a string using repr() and then hex-escapes all non-ASCII
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characters. The ``'%a'`` format operator generates the same string as
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``'%r'`` in Python 2.
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object to a string using repr() and then hex-escapes all non-ASCII
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characters. The ``'%a'`` format operator generates the same string as
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``'%r'`` in Python 2.
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- Add a new built-in function, ``ascii()``. This function converts any
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python object to a string using repr() and then hex-escapes all non-
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ASCII characters. ``ascii()`` generates the same string as ``repr()``
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in Python 2.
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python object to a string using repr() and then hex-escapes all non-
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ASCII characters. ``ascii()`` generates the same string as ``repr()``
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in Python 2.
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- Add an ``isprintable()`` method to the string type. ``str.isprintable()``
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returns False if repr() should escape any character in the string;
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otherwise returns True. The ``isprintable()`` method calls the
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`` Py_UNICODE_ISPRINTABLE()`` function internally.
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returns False if repr() should escape any character in the string;
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otherwise returns True. The ``isprintable()`` method calls the
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`` Py_UNICODE_ISPRINTABLE()`` function internally.
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Rationale
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@ -157,38 +157,38 @@ suggestions were made.
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- Supply a tool to print lists or dicts.
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Strings to be printed for debugging are not only contained by lists or
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dicts, but also in many other types of object. File objects contain a
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file name in Unicode, exception objects contain a message in Unicode,
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etc. These strings should be printed in readable form when repr()ed.
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It is unlikely to be possible to implement a tool to print all
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possible object types.
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Strings to be printed for debugging are not only contained by lists or
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dicts, but also in many other types of object. File objects contain a
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file name in Unicode, exception objects contain a message in Unicode,
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etc. These strings should be printed in readable form when repr()ed.
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It is unlikely to be possible to implement a tool to print all
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possible object types.
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- Use sys.displayhook and sys.excepthook.
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For interactive sessions, we can write hooks to restore hex escaped
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characters to the original characters. But these hooks are called only
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when printing the result of evaluating an expression entered in an
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interactive Python session, and doesn't work for the print() function,
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for non-interactive sessions or for logging.debug("%r", ...), etc.
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For interactive sessions, we can write hooks to restore hex escaped
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characters to the original characters. But these hooks are called only
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when printing the result of evaluating an expression entered in an
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interactive Python session, and doesn't work for the print() function,
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for non-interactive sessions or for logging.debug("%r", ...), etc.
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- Subclass sys.stdout and sys.stderr.
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It is difficult to implement a subclass to restore hex-escaped
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characters since there isn't enough information left by the time it's
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a string to undo the escaping correctly in all cases. For example, ``
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print("\\"+"u0041")`` should be printed as '\\u0041', not 'A'. But
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there is no chance to tell file objects apart.
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It is difficult to implement a subclass to restore hex-escaped
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characters since there isn't enough information left by the time it's
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a string to undo the escaping correctly in all cases. For example, ``
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print("\\"+"u0041")`` should be printed as '\\u0041', not 'A'. But
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there is no chance to tell file objects apart.
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- Make the encoding used by unicode_repr() adjustable, and make the
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existing repr() the default.
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existing repr() the default.
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With adjustable repr(), the result of using repr() is unpredictable
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and would make it impossible to write correct code involving repr().
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And if current repr() is the default, then the old convention remains
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intact and users may expect ASCII strings as the result of repr().
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Third party applications or libraries could be confused when a custom
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repr() function is used.
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With adjustable repr(), the result of using repr() is unpredictable
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and would make it impossible to write correct code involving repr().
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And if current repr() is the default, then the old convention remains
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intact and users may expect ASCII strings as the result of repr().
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Third party applications or libraries could be confused when a custom
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repr() function is used.
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Backwards Compatibility
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@ -234,37 +234,36 @@ Open Issues
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===========
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- Is the ``ascii()`` function necessary, or is it sufficient to document
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how to do it? If necessary, should ``ascii()`` belong to the builtin
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namespace?
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how to do it? If necessary, should ``ascii()`` belong to the builtin
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namespace?
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Rejected Proposals
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==================
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- Add encoding and errors arguments to the builtin print() function,
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with defaults of sys.getfilesystemencoding() and 'backslashreplace'.
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with defaults of sys.getfilesystemencoding() and 'backslashreplace'.
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Complicated to implement, and in general, this is not seen as a good
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idea. [2]_
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Complicated to implement, and in general, this is not seen as a good
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idea. [2]_
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- Use character names to escape characters, instead of hex character
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codes. For example, ``repr('\u03b1')`` can be converted to
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``"\N{GREEK SMALL LETTER ALPHA}"``.
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codes. For example, ``repr('\u03b1')`` can be converted to
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``"\N{GREEK SMALL LETTER ALPHA}"``.
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Using character names can be very verbose compared to hex-escape.
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e.g., ``repr("\ufbf9")`` is converted to ``"\N{ARABIC LIGATURE UIGHUR
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KIRGHIZ YEH WITH HAMZA ABOVE WITH ALEF MAKSURA ISOLATED FORM}"``.
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Using character names can be very verbose compared to hex-escape.
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e.g., ``repr("\ufbf9")`` is converted to ``"\N{ARABIC LIGATURE UIGHUR
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KIRGHIZ YEH WITH HAMZA ABOVE WITH ALEF MAKSURA ISOLATED FORM}"``.
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- Default error-handler of sys.stdout should be 'backslashreplace'.
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Stuff written to stdout might be consumed by another program that
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might misinterpret the \ escapes. For interactive session, it is
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possible to make 'backslashreplace' error-handler to default, but may
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add confusion of the kind "it works in interactive mode but not when
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redirecting to a file".
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Stuff written to stdout might be consumed by another program that
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might misinterpret the \ escapes. For interactive session, it is
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possible to make 'backslashreplace' error-handler to default, but may
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add confusion of the kind "it works in interactive mode but not when
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redirecting to a file".
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- Hide quoted text -
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Reference Implementation
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========================
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