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gap.py
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gap.py
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# -*- coding: utf-8 -*-
r"""
Interface to GAP
Sage provides an interface to the GAP system. This system provides
extensive group theory, combinatorics, etc.
The GAP interface will only work if GAP is installed on your
computer; this should be the case, since GAP is included with Sage.
The interface offers three pieces of functionality:
#. ``gap_console()`` - A function that dumps you into
an interactive command-line GAP session.
#. ``gap(expr)`` - Evaluation of arbitrary GAP
expressions, with the result returned as a string.
#. ``gap.new(expr)`` - Creation of a Sage object that
wraps a GAP object. This provides a Pythonic interface to GAP. For
example, if ``f=gap.new(10)``, then
``f.Factors()`` returns the prime factorization of
`10` computed using GAP.
First Examples
--------------
We factor an integer using GAP::
sage: n = gap(20062006); n
20062006
sage: n.parent()
Gap
sage: fac = n.Factors(); fac
[ 2, 17, 59, 73, 137 ]
sage: fac.parent()
Gap
sage: fac[1]
2
GAP and Singular
----------------
This example illustrates conversion between Singular and GAP via
Sage as an intermediate step. First we create and factor a Singular
polynomial.
::
sage: singular(389)
389
sage: R1 = singular.ring(0, '(x,y)', 'dp')
sage: f = singular('9*x^16-18*x^13*y^2-9*x^12*y^3+9*x^10*y^4-18*x^11*y^2+36*x^8*y^4+18*x^7*y^5-18*x^5*y^6+9*x^6*y^4-18*x^3*y^6-9*x^2*y^7+9*y^8')
sage: F = f.factorize()
sage: print(F)
[1]:
_[1]=9
_[2]=x^6-2*x^3*y^2-x^2*y^3+y^4
_[3]=-x^5+y^2
[2]:
1,1,2
Next we convert the factor `-x^5+y^2` to a Sage
multivariate polynomial. Note that it is important to let
`x` and `y` be the generators of a polynomial ring,
so the eval command works.
::
sage: R.<x,y> = PolynomialRing(QQ,2)
sage: s = F[1][3].sage_polystring(); s
'-x**5+y**2'
sage: g = eval(s); g
-x^5 + y^2
Next we create a polynomial ring in GAP and obtain its
indeterminates::
sage: R = gap.PolynomialRing('Rationals', 2); R
PolynomialRing( Rationals, ["x_1", "x_2"] )
sage: I = R.IndeterminatesOfPolynomialRing(); I
[ x_1, x_2 ]
In order to eval `g` in GAP, we need to tell GAP to view
the variables ``x0`` and ``x1`` as the two
generators of `R`. This is the one tricky part. In the GAP
interpreter the object ``I`` has its own name (which
isn't ``I``). We can access its name using
``I.name()``.
::
sage: _ = gap.eval("x := %s[1];; y := %s[2];;"%(I.name(), I.name()))
Now `x_0` and `x_1` are defined, so we can
construct the GAP polynomial `f` corresponding to
`g`::
sage: R.<x,y> = PolynomialRing(QQ,2)
sage: f = gap(str(g)); f
-x_1^5+x_2^2
We can call GAP functions on `f`. For example, we evaluate
the GAP ``Value`` function, which evaluates `f`
at the point `(1,2)`.
::
sage: f.Value(I, [1,2])
3
sage: g(1,2) # agrees
3
Saving and loading objects
--------------------------
Saving and loading GAP objects (using the dumps method, etc.) is
*not* supported, since the output string representation of Gap
objects is sometimes not valid input to GAP. Creating classes that
wrap GAP objects *is* supported, via simply defining the a
_gap_init_ member function that returns a string that when
evaluated in GAP constructs the object. See
``groups/perm_gps/permgroup.py`` for a nontrivial
example of this.
Long Input
----------
The GAP interface reads in even very long input (using files) in a
robust manner, as long as you are creating a new object.
.. note::
Using ``gap.eval`` for long input is much less robust, and is not
recommended.
::
sage: t = '"%s"'%10^10000 # ten thousand character string.
sage: a = gap(t)
Changing which GAP is used
--------------------------
Use this code to change which GAP interpreter is run. E.g.,
::
import sage.interfaces.gap
sage.interfaces.gap.gap_cmd = "/usr/local/bin/gap"
AUTHORS:
- David Joyner and William Stein: initial version(s)
- William Stein (2006-02-01): modified gap_console command so it uses
exactly the same startup command as Gap.__init__.
- William Stein (2006-03-02): added tab completions: gap.[tab], x =
gap(...), x.[tab], and docs, e.g., gap.function? and x.function?
"""
#*****************************************************************************
# Copyright (C) 2005 William Stein <wstein@gmail.com>
#
# Distributed under the terms of the GNU General Public License (GPL)
#
# This code is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
# General Public License for more details.
#
# The full text of the GPL is available at:
#
# http://www.gnu.org/licenses/
#*****************************************************************************
from .expect import Expect, ExpectElement, FunctionElement, ExpectFunction
from .gap_workspace import gap_workspace_file, prepare_workspace_dir
from sage.cpython.string import bytes_to_str
from sage.env import SAGE_EXTCODE
from sage.misc.misc import is_in_string
from sage.misc.cachefunc import cached_method
from sage.misc.instancedoc import instancedoc
from sage.interfaces.tab_completion import ExtraTabCompletion
from sage.structure.element import ModuleElement
import re
import os
import io
import pexpect
import time
import platform
import string
import warnings
WORKSPACE = gap_workspace_file()
first_try = True
gap_cmd = "gap -r"
if platform.processor() == 'ia64' and os.path.exists('/usr/bin/prctl'):
# suppress unaligned access to 0x..., ip=0x... warnings
gap_cmd = 'prctl --unaligned=silent ' + gap_cmd
def gap_command(use_workspace_cache=True, local=True):
if use_workspace_cache:
if local:
return "%s -L %s"%(gap_cmd, WORKSPACE), False
else:
# TO DO: Use remote workspace
return gap_cmd, False
else:
return gap_cmd, True
############ Classes with methods for both the GAP3 and GAP4 interface
class Gap_generic(ExtraTabCompletion, Expect):
r"""
Generic interface to the GAP3/GAP4 interpreters.
AUTHORS:
- William Stein and David Joyner (interface for GAP4)
- Franco Saliola (Feb 2010): refactored to separate out the generic
code
"""
_identical_function = "IsIdenticalObj"
def _synchronize(self, timeout=0.5, cmd='%s;'):
"""
Synchronize GAP pexpect interface.
See the base method
:meth:`~sage.interfaces.expect.Expect._synchronize` for more
details.
We override this method since we are looking at GAP package
mode output, which is quite different from the normal
(human-readable) interface.
EXAMPLES::
sage: gap('"ok"')
ok
sage: gap._expect.sendline() # now we are out of sync
1
sage: gap._synchronize()
sage: gap(123)
123
"""
if self._expect is None:
return
E = self._expect
from sage.misc.prandom import randrange
rnd = randrange(2147483647)
cmd = str(rnd)+';'
try:
E.sendline(cmd)
E.expect(r'@[nf][@J\s>]*'+str(rnd), timeout=timeout)
E.send(' ')
E.expect('@i', timeout=timeout)
except pexpect.TIMEOUT:
self.interrupt()
except pexpect.EOF:
self._crash_msg()
self.quit()
def interrupt(self, tries=None, timeout=1, quit_on_fail=True):
"""
Interrupt the GAP process
Gap installs a SIGINT handler, we call it directly instead of
trying to sent Ctrl-C. Unlike
:meth:`~sage.interfaces.expect.Expect.interrupt`, we only try
once since we are knowing what we are doing.
Sometimes GAP dies while interrupting.
EXAMPLES::
sage: gap._eval_line('while(1=1) do i:=1;; od;', wait_for_prompt=False)
''
sage: rc = gap.interrupt(timeout=1)
sage: [ gap(i) for i in range(10) ] # check that it is still working
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
TESTS::
sage: gap('"finished computation"'); gap.interrupt(); gap('"ok"')
finished computation
True
ok
"""
E = self._expect
if E is None:
return True
# GAP oddity: If a computation is running and we send Ctrl-C,
# it is stopped as expected. But if we are at the idle prompt,
# nothing is happening UNTIL we run the next command (which is
# then immediately interrupted).
# There is apparently also a race in GAP between the signal
# handler and input, if we don't wait a bit the result is
# unpredictable.
E.sendline(chr(3))
time.sleep(0.1)
E.sendline()
try:
# send a dummy command
E.sendline('224433409;')
# read everything up to the actual output of the command
E.expect(r'@[nf][@J\s>]*224433409', timeout=timeout)
E.send(' ')
# the following input prompt should be the current input
# prompt but GAP might be too confused to display it
# E.expect('@i', timeout=timeout)
# Ideally, we would be finished here. But sometimes GAP
# thinks it is still inside a do/od block. So we run some
# more plain commands to get back into sync. These might
# either complete successfully (output "@n+<number>") or
# return a "Syntax error: od expected@J@f +<number>"
E.sendline()
time.sleep(0.1)
E.sendline('224433437;')
E.expect(r'@[nf][@J\s>]*224433437', timeout=timeout)
E.sendline()
time.sleep(0.1)
E.sendline('224433479;')
E.expect(r'@[nf][@J\s>]*224433479', timeout=timeout)
E.send(' ')
# the following input prompt is now the current input prompt
E.expect('@i', timeout=timeout)
success = True
except (pexpect.TIMEOUT, pexpect.EOF):
# GAP died or hangs indefinitely
success = False
if not success and quit_on_fail:
self.quit()
return success
def _assign_symbol(self):
r"""
Return the assign symbol in GAP.
TESTS::
sage: gap = Gap()
sage: print(gap._assign_symbol())
:=
"""
return ":="
def _quit_string(self):
"""
Returns the string used to quit GAP.
EXAMPLES::
sage: gap._quit_string()
'quit;'
::
sage: g = Gap()
sage: a = g(2); g.is_running()
True
sage: g.quit()
sage: g.is_running()
False
"""
return 'quit;'
def _read_in_file_command(self, filename):
r"""
Returns the command use to read in a file in GAP.
EXAMPLES::
sage: gap._read_in_file_command('test')
'Read("test");'
::
sage: filename = tmp_filename()
sage: with open(filename, 'w') as f:
....: _ = f.write('xx := 22;\n')
sage: gap.read(filename)
sage: gap.get('xx').strip()
'22'
"""
return 'Read("%s");' % filename
def _continuation_prompt(self):
"""
Returns the continuation prompt in GAP.
EXAMPLES::
sage: gap._continuation_prompt()
'> '
"""
return '> '
def load_package(self, pkg, verbose=False):
"""
Load the Gap package with the given name.
If loading fails, raise a RuntimeError exception.
TESTS::
sage: gap.load_package("chevie")
Traceback (most recent call last):
...
RuntimeError: Error loading Gap package chevie. You may want to install gap_packages SPKG.
"""
if verbose:
print("Loading GAP package {}".format(pkg))
x = self.eval('LoadPackage("{}")'.format(pkg))
if x == 'fail':
raise RuntimeError("Error loading Gap package "+str(pkg)+". "+
"You may want to install gap_packages SPKG.")
def eval(self, x, newlines=False, strip=True, split_lines=True, **kwds):
r"""
Send the code in the string s to the GAP interpreter and return the
output as a string.
INPUT:
- ``s`` - string containing GAP code.
- ``newlines`` - bool (default: True); if False,
remove all backslash-newlines inserted by the GAP output
formatter.
- ``strip`` - ignored
- ``split_lines`` -- bool (default: True); if True then each
line is evaluated separately. If False, then the whole
block of code is evaluated all at once.
EXAMPLES::
sage: gap.eval('2+2')
'4'
sage: gap.eval('Print(4); #test\n Print(6);')
'46'
sage: gap.eval('Print("#"); Print(6);')
'#6'
sage: gap.eval('4; \n 6;')
'4\n6'
sage: gap.eval('if 3>2 then\nPrint("hi");\nfi;')
'hi'
sage: gap.eval('## this is a test\nPrint("OK")')
'OK'
sage: gap.eval('Print("This is a test. Oh no, a #");# but this is a comment\nPrint("OK")')
'This is a test. Oh no, a #OK'
sage: gap.eval('if 4>3 then')
''
sage: gap.eval('Print("Hi how are you?")')
'Hi how are you?'
sage: gap.eval('fi')
''
TESTS:
Whitespace is not stripped from the front of the result
(:trac:`28439`)::
sage: gap.eval(r'Print(" -\n\\\\- ")')
' -\n\\\\-'
"""
# '"
#We remove all of the comments: On each line, we try
#to find a pound sign. If we find it, we check to see if
#it is occurring in a string. If it is not in a string, we
#strip off the comment.
if not split_lines:
input_line=str(x)
else:
input_line = ""
for line in str(x).rstrip().split('\n'):
pound_position = line.find('#')
while pound_position != -1:
if not is_in_string(line, pound_position):
line = line[:pound_position]
pound_position = line.find('#',pound_position+1)
input_line += " "+line
if not input_line.endswith(';'):
input_line += ';'
result = Expect.eval(self, input_line, **kwds)
if not newlines:
result = result.replace("\\\n","")
return result.rstrip()
def _execute_line(self, line, wait_for_prompt=True, expect_eof=False):
if self._expect is None: # interface is down
self._start()
E = self._expect
try:
if len(line) > 4095:
raise RuntimeError("Passing commands this long to gap would hang")
E.sendline(line)
except OSError:
raise RuntimeError("Error evaluating %s in %s"%(line, self))
if not wait_for_prompt:
return (b'',b'')
if len(line)==0:
return (b'',b'')
try:
terminal_echo = [] # to be discarded
normal_outputs = [] # GAP stdout
error_outputs = [] # GAP stderr
current_outputs = terminal_echo
while True:
x = E.expect_list(self._compiled_full_pattern)
current_outputs.append(E.before)
if x == 0: # @p
if E.after != b'@p1.':
warnings.warn(
"possibly wrong version of GAP package "
"interface. Crossing fingers and continuing.")
elif x == 1: #@@
current_outputs.append(b'@')
elif x == 2: #special char
c = ord(E.after[1:2]) - ord(b'A') + 1
s = bytes([c])
current_outputs.append(s)
elif x == 3: # garbage collection info, ignore
pass
elif x == 4: # @e -- break loop
E.sendline("quit;")
elif x == 5: # @c completion, doesn't seem to happen when -p is in use
warnings.warn("I didn't think GAP could do this")
elif x == 6: # @f GAP error message
current_outputs = error_outputs
elif x == 7: # @h help text, but this stopped happening with new help
warnings.warn("I didn't think GAP could do this")
elif x == 8: # @i awaiting normal input
break
elif x == 9: # @m finished running a child
pass # there is no need to do anything
elif x==10: #@n normal output line
current_outputs = normal_outputs
elif x==11: #@r echoing input
current_outputs = terminal_echo
elif x==12: #@sN shouldn't happen
warnings.warn("this should never happen")
elif x==13: #@w GAP is trying to send a Window command
warnings.warn("this should never happen")
elif x ==14: #@x seems to be safely ignorable
pass
elif x == 15:#@z GAP starting a subprocess
pass # there is no need to do anything
except pexpect.EOF:
if not expect_eof:
raise RuntimeError("Unexpected EOF from %s executing %s"%(self,line))
except IOError:
raise RuntimeError("IO Error from %s executing %s"%(self,line))
return (b"".join(normal_outputs), b"".join(error_outputs))
def _keyboard_interrupt(self):
"""
TESTS:
We check that the gap interface behaves correctly after an
interrupt::
sage: gap(2)
2
sage: try:
....: alarm(0.5)
....: gap.eval('while(1=1) do i:=1;; od;', wait_for_prompt=True)
....: except KeyboardInterrupt:
....: pass
sage: gap(2)
2
"""
self.quit()
raise KeyboardInterrupt("Ctrl-c pressed while running %s"%self)
def _eval_line(self, line, allow_use_file=True, wait_for_prompt=True, restart_if_needed=True):
r"""
Evaluate a line of commands.
REMARK:
By default, a long command (length exceeding ``self._eval_using_file_cutoff``)
is evaluated using :meth:`_eval_line_using_file`.
If the command can not be evaluated since the interface
has crashed, it is automatically restarted and tried
again *once*.
If the optional ``wait_for_prompt`` is ``False`` then even a very long line
will not be evaluated by :meth:`_eval_line_using_file`, since this does not
support the ``wait_for_prompt`` option.
INPUT:
- ``line`` -- (string) a command.
- ``allow_use_file`` (optional bool, default ``True``) --
allow to evaluate long commands using :meth:`_eval_line_using_file`.
- ``wait_for_prompt`` (optional bool, default ``True``) --
wait until the prompt appears in the sub-process' output.
- ``restart_if_needed`` (optional bool, default ``True``) --
If it is ``True``, the command evaluation is evaluated
a second time after restarting the interface, if an
``EOFError`` occurred.
TESTS::
sage: gap._eval_line('2+2;')
'4'
We test the ``wait_for_prompt`` option by sending a command that
creates an infinite loop in the GAP sub-process. But if we don't
wait for the prompt to appear in the output, we can interrupt
the loop without raising a KeyboardInterrupt. At the same time,
we test that the line is not forwarded to :meth:`_eval_line_using_file`,
since that method would not support the ``wait_for_prompt`` option::
sage: cutoff = gap._eval_using_file_cutoff
sage: gap._eval_using_file_cutoff = 4
sage: gap._eval_line('while(1=1) do i:=1;; od;', wait_for_prompt=False)
''
sage: rc = gap.interrupt(timeout=1)
sage: gap._eval_using_file_cutoff = cutoff
The following tests against a bug fixed at :trac:`10296`::
sage: gap(3)
3
sage: gap.eval('quit;')
''
sage: a = gap(3)
** Gap crashed or quit executing '\$sage...:=3;;' **
Restarting Gap and trying again
sage: a
3
"""
expect_eof = self._quit_string() in line
try:
if self._expect is None:
self._start()
if allow_use_file and wait_for_prompt and len(line) > self._eval_using_file_cutoff:
return self._eval_line_using_file(line)
(normal, error) = self._execute_line(line, wait_for_prompt=wait_for_prompt,
expect_eof=expect_eof)
# The internal method _execute_line returns bytes but the bytes it
# returns should contain text (any terminal commands and other
# garbage should be filtered out by this point); here we decode
# them (on Python 3), currently just using the default encoding
normal, error = bytes_to_str(normal), bytes_to_str(error)
if error:
if 'Error, Rebuild completion files!' in error:
error += "\nRunning gap_reset_workspace()..."
self.quit()
gap_reset_workspace()
error = error.replace('\r','')
raise RuntimeError("%s produced error output\n%s\n executing %s"%(self, error,line))
if not normal:
return ''
if isinstance(wait_for_prompt, str) and normal.ends_with(wait_for_prompt):
n = len(wait_for_prompt)
elif normal.endswith(bytes_to_str(self._prompt)):
n = len(self._prompt)
elif normal.endswith(self._continuation_prompt()):
n = len(self._continuation_prompt())
else:
n = 0
out = normal[:-n]
if out and out[-1] == "\n":
out = out[:-1]
return out
except (RuntimeError, TypeError, pexpect.ExceptionPexpect) as exc:
if not self._isalive():
# We can't distinguish just EOF from an unexpectedly killed
# process because pexpect catches EOF's and re-reraises them
# But if we *were* expecting EOF then we should just let it
# fail silently and return
if expect_eof:
return ''
print("** %s crashed or quit executing '%s' **" % (self, line))
print("Restarting %s and trying again" % self)
self._start()
if line != '':
return self._eval_line(line, allow_use_file=allow_use_file)
else:
return ''
else:
raise RuntimeError(exc)
except KeyboardInterrupt:
self._keyboard_interrupt()
raise KeyboardInterrupt("Ctrl-c pressed while running %s"%self)
def unbind(self, var):
"""
Clear the variable named var.
EXAMPLES::
sage: gap.set('x', '2')
sage: gap.get('x')
'2'
sage: gap.unbind('x')
sage: gap.get('x')
Traceback (most recent call last):
...
RuntimeError: Gap produced error output
Error, Variable: 'x' must have a value
...
"""
self.eval('Unbind(%s)'%var)
self.clear(var)
def _contains(self, v1, v2):
"""
EXAMPLES::
sage: Integers = gap('Integers')
sage: two = gap(2)
sage: gap._contains(two.name(), Integers.name())
True
::
sage: 2 in gap('Integers')
True
"""
return self.eval('%s in %s'%(v1,v2)) == "true"
def _true_symbol(self):
"""
Returns the symbol for truth in GAP.
EXAMPLES::
sage: gap._true_symbol()
'true'
sage: gap(2) == gap(2)
True
"""
return "true"
def _false_symbol(self):
"""
Returns the symbol for falsity in GAP.
EXAMPLES::
sage: gap._false_symbol()
'false'
sage: gap(2) == gap(3)
False
"""
return "false"
def _equality_symbol(self):
"""
Returns the symbol for equality in GAP.
EXAMPLES::
sage: gap._equality_symbol()
'='
sage: gap(2) == gap(3)
False
sage: gap(2) == gap(2)
True
"""
return "="
def version(self):
"""
Returns the version of GAP being used.
EXAMPLES::
sage: print(gap.version())
4...
"""
return self.eval('GAPInfo.Version')[1:-1]
def function_call(self, function, args=None, kwds=None):
"""
Calls the GAP function with args and kwds.
EXAMPLES::
sage: gap.function_call('SymmetricGroup', [5])
SymmetricGroup( [ 1 .. 5 ] )
If the GAP function does not return a value, but prints something
to the screen, then a string of the printed output is returned.
::
sage: s = gap.function_call('Display', [gap.SymmetricGroup(5).CharacterTable()])
sage: type(s)
<class 'sage.interfaces.interface.AsciiArtString'>
sage: s.startswith('CT')
True
TESTS:
If the function call is too long, two ``gap.eval`` calls are made
since returned values from commands in a file cannot be handled
properly::
sage: g = Gap()
sage: g.function_call("ConjugacyClassesSubgroups", sage.interfaces.gap.GapElement(g, 'SymmetricGroup(2)', name = 'a_variable_with_a_very_very_very_long_name')) # random
[ ConjugacyClassSubgroups(SymmetricGroup( [ 1 .. 2 ] ),Group( () )),
ConjugacyClassSubgroups(SymmetricGroup( [ 1 .. 2 ] ),Group( [ (1,2) ] )) ]
When the command itself is so long that it warrants use of a temporary
file to be communicated to GAP, this does not cause problems since
the file will contain a single command::
sage: g.function_call("ConjugacyClassesSubgroups", sage.interfaces.gap.GapElement(g, 'SymmetricGroup(2)', name = 'a_variable_with_a_name_so_very_very_very_long_that_even_by_itself_will_make_expect_use_a_file')) # random
[ ConjugacyClassSubgroups(SymmetricGroup( [ 1 .. 2 ] ),Group( () )),
ConjugacyClassSubgroups(SymmetricGroup( [ 1 .. 2 ] ),Group( [ (1,2) ] )) ]
"""
args, kwds = self._convert_args_kwds(args, kwds)
self._check_valid_function_name(function)
#Here we have to do some magic because not all GAP
#functions return a value. If you try to store their
#results to a variable, then GAP will complain. Thus, before
#we evaluate the function, we make it so that the marker string
#is in the 'last' variable in GAP. If the function returns a
#value, then that value will be in 'last', otherwise it will
#be the marker.
marker = '__SAGE_LAST__:="__SAGE_LAST__";;'
cmd = "%s(%s);;"%(function, ",".join([s.name() for s in args]+
['%s=%s'%(key,value.name()) for key, value in kwds.items()]))
if len(marker) + len(cmd) <= self._eval_using_file_cutoff:
# We combine the two commands so we only run eval() once and the
# only output would be from the second command
res = self.eval(marker+cmd)
else:
self.eval(marker)
res = self.eval(cmd)
if self.eval(self._identical_function + '(last,__SAGE_LAST__)') != 'true':
return self.new('last2;')
else:
if res.strip():
from sage.interfaces.interface import AsciiArtString
return AsciiArtString(res)
def get_record_element(self, record, name):
r"""
Return the element of a GAP record identified by ``name``.
INPUT:
- ``record`` -- a GAP record
- ``name`` -- str
OUTPUT:
- :class:`GapElement`
EXAMPLES::
sage: rec = gap('rec( a := 1, b := "2" )')
sage: gap.get_record_element(rec, 'a')
1
sage: gap.get_record_element(rec, 'b')
2
TESTS::
sage: rec = gap('rec( a := 1, b := "2" )')
sage: type(gap.get_record_element(rec, 'a'))
<class 'sage.interfaces.gap.GapElement'>
"""
return self('%s.%s' % (record.name(), name))
# We need to inherit from ModuleElement to support
# sage.structure.coerce_actions.ModuleAction and it needs to be first
# in the MRO because extension types should always come first.
@instancedoc
class GapElement_generic(ModuleElement, ExtraTabCompletion, ExpectElement):
r"""
Generic interface to the GAP3/GAP4 interpreters.
AUTHORS:
- William Stein and David Joyner (interface for GAP4)
- Franco Saliola (Feb 2010): refactored to separate out the generic
code
"""
def _add_(self, other):
"""
EXAMPLES::
sage: a = gap(1)
sage: a + a
2
"""
# This is just a copy of ExpectElement._add_ to fix the fact
# that the abtract method ModuleElement._add_ comes first in
# the MRO.
return self._operation("+", other)
def __bool__(self):
"""
EXAMPLES::
sage: bool(gap(2))
True
sage: gap(0).bool()
False
sage: gap('false').bool()
False
"""
P = self._check_valid()
return self != P(0) and repr(self) != 'false'
def __len__(self):
"""
EXAMPLES::
sage: v = gap('[1,2,3]'); v
[ 1, 2, 3 ]
sage: len(v)
3
len is also called implicitly by if::
sage: if gap('1+1 = 2'):
....: print("1 plus 1 does equal 2")
1 plus 1 does equal 2
::
sage: if gap('1+1 = 3'):
....: print("it is true")
....: else:
....: print("it is false")
it is false
"""
P = self.parent()
if P.eval('%s = true'%self.name()) == 'true':
return 1
elif P.eval('%s = false'%self.name()) == 'true':
return 0
else:
return int(self.Length())
def is_string(self):
"""
Tell whether this element is a string.
EXAMPLES::
sage: gap('"abc"').is_string()
True
sage: gap('[1,2,3]').is_string()
False
"""
return bool(self.IsString())
def _matrix_(self, R):
r"""
Return matrix over the (Sage) ring R determined by self, where self
should be a Gap matrix.
EXAMPLES::
sage: s = gap("(Z(7)^0)*[[1,2,3],[4,5,6]]"); s
[ [ Z(7)^0, Z(7)^2, Z(7) ], [ Z(7)^4, Z(7)^5, Z(7)^3 ] ]
sage: s._matrix_(GF(7))
[1 2 3]
[4 5 6]
::