pypre

A python preprocessor

This package is meant to pre-process raw python 3 files.

Usage

pypre [ -i INPUT_FILE or --input INPUT_FILE ] [ -o OUTPUT_FILE --output OUTPUT_FILE ]

If an input file is not given, pypre will read input on stdin. Likewise, if an output file is not given, pypre will write output to stdout.

Syntax

The syntax for the preprocessor is fairly simple:

• #define <CONST> [<VALUE>]

  This defines a new constant name "CONST", optionally with the value "VALUE". If a VALUE is not specified, "CONST" will be assigned the value None. "VALUE" must be a python literal value. The primitive objects currently supported are:

  • int
  • float
  • str
  • bytes
    This also includes the following primitive collections of these types:
  • list
  • tuple
  • dict
  • set
    Finally, values MUST be literal. pypre cannot and will not interpret #defines that include #defined constant names.
    Just like the C/C++ preprocessor, anywhere a #defined constant is found within the source code (except on lines containing directives) it will be replaced with its value.
    WARNING: This does not yet check whether names are inside of string literals or comments.

• #undef <CONST>

  Removes the definition of the name specified by "CONST". If the name wasn't defined in the first place, nothing happens (or at least it shouldn't).

• #ifdef <CONST>

  Begins a block of conditionally-compiled code. All code up to the matching terminator will be included in the output if and only if the constant named by "CONST" has been defined. (see #endif)

• #ifndef <CONST>

  Provided mainly for historical reasons, this begins a block of conditionally-compiled code similar to #ifdef, but will include the enclosed block if and only if the named constant "CONST" is not defined.

• #if <EXPR>

  The real meat of pypre. This begins a block of conditionally-compiled code based on the truth-y value of "EXPR". "EXPR" can take two forms. In the first form, it takes a single value. It can be - somewhat uselessly - a python literal that would be valid as the "VALUE" of a #define, or it can be the name of a previously-#defined value. In its second form, "EXPR" looks like: <VALUE> <OP> <VALUE> Where each "VALUE" is anything that would be valid for a "VALUE" in the first form, and "OP" is a boolean operator. Valid operators and their definition are:

  • =

  The Equality Operator - tests that the two values are equal.

  • !

  The Inequality Operator - tests that the two values are NOT equal.

  • <

  The Less-Than Operator - tests that the first value is strictly less than the second.

  • >

  The Greater-Than Operator - tests that the first value is strictly greater than the second.

• #else

  If found within a block of conditionally-compiled code, will begin a section of conditionally-code that will be included if and only if the lines between the directive that started the block and the line containing #else are not included.

• #endif

  Ends a block of conditionally-compiled code. For every #if, #ifdef and ifndef, there must be exactly one #endif.

Guaranteed Values

The following values are defined at runtime, and can be overridden with an environment variable of the same name:

• PYTHON_VERSION

  A tuple of the form "(MAJOR, MINOR, MICRO)" where each element is of type int. It will default to the version information of the interpreter used to run pypre. Setting this will set PYTHON_MAJOR_VERSION, PYTHON_MINOR_VERSION, and PYTHON_MICRO_VERSION accordingly.

• PYTHON_MAJOR_VERSION

  An int representing a Python major version number. Will default to the major version number of the interpreter used to run pypre. If you set this variable through the environment variable of the same name, it will set PYTHON_MINOR_VERSION and PYTHON_MICRO_VERSION both to 0 (unless those are set as well, in which case they will use their defined values).

• PYTHON_MINOR_VERSION

  An int representing a Python minor version number. Will default to the minor version number of the interpreter used to run pypre. If you set this variable through the environment variable of the same name, it will set PYTHON_MAJOR_VERSION to 3 and PYTHON_MICRO_VERSION to 0. (unless those are set as well, in which case they will use their defined values).

• PYTHON_MICRO_VERSION

  An int representing a Python micro version number. Will default to the micro version number of the interpreter used to run pypre. If you set this variable through the environment variable of the same name, it will set PYTHON_MAJOR_VERSION to 3 and PYTHON_MINOR_VERSION to 0. (unless those are set as well, in which case they will use their defined values).

• PYTHON_IMPLEMENTATION

  A str that names the Python implementation. Defaults to the output of platform.python_implementation(). Some examples include: ‘CPython’, ‘IronPython’, ‘Jython’, ‘PyPy’.

• OS

  A str naming the operating system. Defaults to the sysname part of the output of os.uname().

• ARCH

  A string specifying the system's architecture. Defaults to the output of platform.machine()

• IS64

  True if the host processor is 64-bit, otherwise False. Default is determined using the bits part of the output of platform.architecture().

• __DATE__

  A literal str containing the date on which the pre-processing is occurring, in the same format as the C++ macro of the same name: "Mmm dd yyyy". The default value is obtained from the output of time.strftime("%b %d %Y").

• __TIME__

  A literal str containing the local time at which the pre-processing is occurring, in the same format as the C++ macro of the same name: "hh:mm:ss". The default value is obtained from the output of time.strftime("%H:%M:%S").

• __IPV6__

  True if the system supports IPv6 addressing, False otherwise. Default value is obtained from the value of socket.has_ipv6.

• __BYTE_ORDER__

  This is a value representing the native byte order of the host machine. Its default value is calculated using the struct library and it has no particular guaranteed value. The only thing that can be depended upon is that it will be equal to either __BIG_ENDIAN__ or __LITTLE_ENDIAN__; never both and never neither. Implementation Note: As of the time of this writing, __BIG_ENDIAN__ is set to the value 1 and __LITTLE_ENDIAN__ is set to the value 0. This is subject to change as I may need to specify the endian-ness of bits or gods only knows what else in the future.

Note that if you do choose to override these values, you MUST match their type. For example, if the name FOO is provided with a value of (b'\x69', 15.2), you must provide a value that is a 2-tuple of the form (bytes, float). In bash, this example would look like:

FOO="(b'my overridden bytes', -1.1)" pypre

Some caveats and disclaimers:

• Do not use spaces in your names or values (except between elements in collections) as this will instantly crash the preprocessor.
• pypre is only built for, and only tested against Python 3 versions. Don't be surprised if it doesn't work if run through your Python 2 interpreter. (Note that you can easily include pypre directives in Python 2 code as long as pypre itself is run through Python 3, although it will require you to set PYTHON_VERSION yourself if you plan to use it.)
• Setting PYTHON_VERSION and one of the more specific "MAJOR"/"MINOR"/"MICRO" variables to non-compatible values will cause the preprocessor to immediately exit. For example, you can't have PYTHON_VERSION=(2,7,0) and PYTHON_MAJOR_VERSION=3 - be sure your environment makes sense.