Access std::complex<> from gdb python macro - c++

Question

I'm trying to write a python script that evaluates a vector Complex numbers so I can do things like plot it via matplotlib. Python code below with comment where code breaks:
import sys
import gdb
import matplotlib.pyplot as plt
class Plotter (gdb.Command):
""" Plots vector"""
# _iterator pulled directly from
# /usr/share/gdb/python/libstdcxx/v6/printers.py
class _iterator:
def __init__ (self, start, finish):
self.item = start
self.finish = finish
self.count = 0
def __iter__(self):
return self
def next(self):
if self.item == self.finish:
raise StopIteration
count = self.count
self.count = self.count + 1
elt = self.item.dereference()
self.item = self.item + 1
return ('[%d]' % count, elt)
def __init__(self):
super(Plotter, self).__init__("plot_test", gdb.COMMAND_OBSCURE)
def invoke(self, arg, from_tty):
frame = gdb.selected_frame()
try:
val = gdb.Frame.read_var(frame, arg)
if str(val.type).find("vector") != -1:
print "Plot vector:", str(val.type)
if (str(val.type).find("complex") != -1):
self.plot_complex_vector(val)
else:
self.plot_vector(val)
else:
print "Not a vector..."
except:
print "No such variable:", arg
return
def plot_complex_vector(self, val):
try:
it = self._iterator(val['_M_impl']['_M_start'],
val['_M_impl']['_M_finish'])
vector = []
while(True):
x = it.next()
vector.append(complex(x[1])) # doesn't work...
return
except StopIteration:
pass
except:
print sys.exc_info()[0]
print vector
plt.plot(vector)
plt.show()
# works...
def plot_vector(self, val):
try:
it = self._iterator(val['_M_impl']['_M_start'],
val['_M_impl']['_M_finish'])
vector = []
while(True):
x = it.next()
vector.append(float(x[1]))
except StopIteration:
pass
except:
print sys.exc_info()[0]
print vector
plt.plot(vector)
plt.show()
Plotter()
So the question is, how do I access the real/imaginary parts of a a std::complex value?
It looks like doing a
print x[1]
Will print values like : {_M_value = 0 + 1 * I}
Update: It looks like I can do a little string editing before doing a typecast:
while(True):
x = it.next()
s = str(x[1]['_M_value'])
# convert string to complex format that python understands.
c = complex(s.replace('I','j').replace(' ','').replace('*',''))
vector.append(c) # Works now...
But... is there a better way to do this?

Answer 1

try:
it = self._iterator(val['_M_impl']['_M_start'],
val['_M_impl']['_M_finish'])
vector = []
while(True):
x = it.next()
vector.append(complex(x[1])) # doesn't work...
return
except StopIteration:
pass
except:
print sys.exc_info()[0]
Is not how iterators are meant to be used in python. Use
try:
it = self._iterator(val['_M_impl']['_M_start'],
val['_M_impl']['_M_finish'])
vector = [complex(x[1]) for x in it]
except Exception as e:
print e, sys.exc_info()[0]
If you really still want to wrap it in a try...except block.
Edit: Try complex(x.real() + x.imag()). What does print x.type.fields() show?