Metadata-Version: 1.0
Name: pyfil
Version: 0.4
Summary: print the return value of python expression -- also in loops
Home-page: https://github.com/ninjaaron/pyfil
Author: Aaron Christianson
Author-email: ninjaaron@gmail.com
License: BSD
Description: pyfil
        =====
        This ain't the first project of this kind, and it won't be the last, but
        this one is special because it's all mine. ``pyeval`` is a more
        mature project of a similar sort. Some might accuse ``pyeval`` of
        feature creep, but I would never do that, because I'm totally not
        jealous that they did it first. :D
        
        Pretty sure there are other projects like this, too. It's sort of an
        obvious thing to try to do: Python one-liners in the spirit of Perl and
        AWK.
        
        ``pyfil`` gives you the ``rep`` command. This is because when I
        initially posted it in #python IRC channel, user [Tritium] (that ray of
        sunshine) said I had recreated the REP of the python REPL (read evaluate
        print loop). That is more or less the case. ``rep`` reads python
        expressions at the command line, evaluates them and prints them to
        stdout. It might be interesting as a quick calculator or to test
        something, like the Python REPL, but it also has some special flags for
        iterating on stdin and parsing JSON, which make it useful as a filter
        for shell one-liners or scripts (like Perl).
        
        pyfil is in pypi (i.e. you can get it easily with pip, if you want)
        
        usage
        -----
        
        available objects
        ~~~~~~~~~~~~~~~~~
        Automatically imports (unless overridden in ~/.config/pyfil-env.py):
        
        ``sys``, ``os``, ``re``, ``math``, ``pprint from pprint``, ``timeit
        from timeit`` and ``strftime from time``.
        
        If you'd like to specify a custom execution environment for rep, create
        ~/.config/pyfil-env.py and put things in it.
        
        The execution environment also has a special object for stdin,
        creatively named ``stdin``. This differs from sys.stdin in that it
        rstrips (aka chomps) all the lines when you iterate over it, and it has
        a property, ``stdin.l``, which returns a list of the (rstripped) lines.
        pyfil is quite bullish about using rstrip because python's print
        function will supply an additional newline, and if you just want the
        value of the text in the line, you almost never want the newline
        character. If you do want the newlines, access sys.stdin directly.
        
        stdin inherits the rest of its methods from sys.stdin, so you can use
        stdin.read() to get a string of all lines, if that's what you need.
        
        looping over stdin
        ~~~~~~~~~~~~~~~~~~
        one can do simple loops with a generator expression. (note that any
        expression that evaluates to an iterator will print each item on a new
        line unless the ``--join`` option is specified.)
        
        .. code:: bash
        
            $ ls / | rep '(i.upper() for i in stdin)'
            BIN@
            BOOT/
            DEV/
            ETC/
            HOME/
            ...
        
        However, the ``-l``/``--loop`` flag rep loops over stdin in a context
        like this:
        
        .. code:: python
        
            for i in map(str.rstrip, sys.stdin):
                expressions
        
        Therefore, the above loop can also be written thusly:
        
        .. code:: bash
        
            $ ls / | rep -l 'i.upper()'
        
        ``--pre`` and ``--post`` (-b and -e) options can be used to specify
        actions to run before or after the loop. Note that the --pre option is
        run with exec instead of eval, and therefore output is never printed,
        and statements may be used. This is for things like initializing
        container types. --post is automatically printed and statements are not
        allowed (unless --quiet is used). --loop is implied if either of these
        options are used.
        
        Using ``-s``/``--split`` or ``-F``/``--field-sep`` for doing awk things
        also implies --loop. The resulting list is named ``f`` in the execution
        environment, in quazi-Perl fashion. (oh, and that list is actually a
        subclass of collections.UserList that returns an empty string if the
        index doesn't exist, so it acts more like awk with empty fields, rather
        than throwing and error and interupting iteration).
        
        formatting output
        ~~~~~~~~~~~~~~~~~
        It's probably obvious that the most powerful way to format strings is
        with Python's str.format method and the ``-F`` or ``-s`` options (see
        end of previous section or use --help).
        
        .. code:: bash
        
          $ ls -l /|rep -s '"{0}\t{2}\t{8}".format(*f)' 
          Error: tuple index out of range
          lrwxrwxrwx	root	bin
          drwxr-xr-x	root	boot/
          drwxr-xr-x	root	dev/
          drwxr-xr-x	root	etc/
          drwxr-xr-x	root	home/
          lrwxrwxrwx	root	lib
          ...
        
        However, you will note that using ``string.format(*f)`` produces an
        error and does not print anything to stdout (error message is sent to
        stderr; see error handling for more options) for lines without enough
        fields, which may not be the desired behavior when dealing with lines
        containing arbitrary numbers of fields.
        
        For simpler cases, you may wish to use the ``-n``/``--join`` option,
        which will join any iterables with the specified string before printing,
        and, in the case of the ``f`` list, will replace any none-existant
        fields with an empty string.
        
        .. code:: bash
        
          $ ls -l /|rep -sn '\t' 'f[0], f[2], f[8]'
          total		
          lrwxrwxrwx	root	bin
          drwxr-xr-x	root	boot/
          drwxr-xr-x	root	dev/
          drwxr-xr-x	root	etc/
          drwxr-xr-x	root	home/
          lrwxrwxrwx	root	lib
        
        In this case, the first line of ``ls -l /`` provides values for all
        available fields.
        
        Technical note:
            The separator specified with the ``--join`` option is implemented
            internally as ``ast.literal_eval("'''"+STRING.replace("'",
            r"\'")+"'''", {})``. If one works hard at it, it is possible to pass
            values which will cause pyfil to crash; i.e. patterns ending with a
            backslash. Keep in mind rules about escape squences in the shell and
            in python if you absoulely must have a pattern that terminates with
            a backslash. (The reason it is implemented this way is to allow the
            use of escape sequences that are meaningful to the python, but not
            the shell, such as \n, \t, \x, \u, etc.)
        
        suppressing output and using statements
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
        by default, pyfil prints the return value of expressions. Because this
        uses eval() internally to get value, statements may not be used. exec()
        supports statements, but it does not return the value of expressions
        when they are evaluated. When the -q/--quiet flag is used, automatic
        printing is suppressed, and expressions are evaluated with exec, so
        statements, such as assignments, may be used. Values may still be
        printed explicitely.
        
        error handling
        ~~~~~~~~~~~~~~
        If pyfil encounters an exception while evaluating user input the default
        is to print the error message to stderr and continue (if looping over
        stdin), as we saw in the section on formatting output. However, errors
        can also be silenced entirely with the ``-S``/``--silence-errors``
        option. In the below example, the first line produces an error, but we
        don't hear about it.
        
        .. code:: bash
        
          $ ls -l /|rep -sS '"{0}\t{2}\t{8}".format(*f)' 
          lrwxrwxrwx	root	bin
          drwxr-xr-x	root	boot/
          drwxr-xr-x	root	dev/
          drwxr-xr-x	root	etc/
          drwxr-xr-x	root	home/
          lrwxrwxrwx	root	lib
          ...
        
        Alternatively, errors may be raised when encountered, which will stop
        execution and give a (fairly useless, in this case) traceback. This is
        done with the ``-R``/``--raise-errors`` flag.
        
        .. code:: bash
        
          $ ls -l /|rep -sR '"{0}\t{2}\t{8}".format(*f)'
          Traceback (most recent call last):
            File "/home/ninjaaron/src/py/pyfil/venv/bin/rep", line 9, in <module>
              load_entry_point('pyfil', 'console_scripts', 'rep')()
            File "/home/ninjaaron/src/py/pyfil/pyfil/pyfil.py", line 242, in main
              run(expressions, a, namespace)
            File "/home/ninjaaron/src/py/pyfil/pyfil/pyfil.py", line 164, in run
              handle_errors(e, args)
            File "/home/ninjaaron/src/py/pyfil/pyfil/pyfil.py", line 134, in handle_errors
              raise exception
            File "/home/ninjaaron/src/py/pyfil/pyfil/pyfil.py", line 162, in run
              value = func(expr, namespace)
            File "<string>", line 1, in <module>
          IndexError: tuple index out of range
        
        In addition to these two handlers, it is possible to specify a
        rudimentary custom handler with the ``-H``/``--exception-handler``
        flags. The syntax is ``-H 'Exception: expression'``, where ``Exception``
        can be any builtin exception class (including Exception, to catch all
        errors), and ``expression`` is the alternative expression to evaluate
        (and print, if not --quiet).
        
        .. code:: bash
        
          $ ls -l /|rep -sH 'IndexError: i' '"{0}\t{2}\t{8}".format(*f)'
          total 32
          lrwxrwxrwx	root	bin
          drwxr-xr-x	root	boot/
          drwxr-xr-x	root	dev/
          drwxr-xr-x	root	etc/
          drwxr-xr-x	root	home/
          lrwxrwxrwx	root	lib
          ...
        
        In this case, we've chosen to print line without any additional
        formatting. If other errors are encountered, it will fall back to other
        handlers (``-S``, ``-R``, or the default). For more sophisticated error
        handling... Write a real Python script, where you can handle to your
        heart's content.
        
        json
        ~~~~
        by popular demand, pyfil can parse json objects from stdin with the
        ``-j``/``--json`` flag. They are passed into the environment as the
        ``j`` object.  combining with the --loop flag will treat stdin as one json
        object per line.
        
Keywords: evaluate
Platform: UNKNOWN
