preparser state for regexs

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This works for me from the command line. In the notebook, it fails the first time and succeeds the second time. Indeed, having a notebook cell containing

preparser(False)
type(2)

fails the first time I evaluate it and succeeds the second time. This is what is supposed to happen, though. Consider this, from the command-line:

sage: preparser(False); type(2)

The first thing that happens is that the whole line gets preparsed, so "2" gets turned into "Integer(2)". Then the line gets evaluated, so it turns the preparser off and it returns the type of "Integer(2)", namely sage.rings.integer.Integer. I think that the same thing happens in each cell of the notebook: the whole thing gets preparsed before any of it is evaluated. So you need to put preparser(False) in a separate cell and evaluate it first.

I had a similar issue dealing with the preparser so I wrote an IPython extension which adds a cell magic %%noparse which disables the Sage preparser for the cell its applied to.

Save this code as noparse.py:

from IPython.core.magic import (Magics, magics_class, cell_magic)

import sage.repl.interpreter

@magics_class
class NoParseMagic(Magics):

    @cell_magic
    def noparse(self, line, cell):
        """
        Use this cell magic to disable Sage preparsing in an IPython cell.
        """
        sage.repl.interpreter._do_preparse = False
        self.shell.run_cell(cell)
        sage.repl.interpreter._do_preparse = True

def load_ipython_extension(ipython):
    ipython.register_magics(NoParseMagic)

If you like, you can copy this to .ipython/extensions/. Then in a Sage Jupyter notebook, you can run:

%load_ext noparse

to load the extension. Now the following works:

%%noparse
type(4)

which yields:

<type 'int'>

instead of:

<type 'sage.rings.integer.Integer'>