Cython - iterate through map

Question

I was wondering if this was possible to iterate through a map directly in Cython code, ie, in the .pyx. Here is my example:

import cython
cimport cython
from licpp.map import map as mapcpp

def it_through_map(dict mymap_of_int_int):
  # python dict to map
  cdef mapcpp[int,int] mymap_in = mymap_of_int_int
  cdef mapcpp[int,int].iterator it = mymap_in.begin()

  while(it != mymap.end()):
    # let's pretend here I just want to print the key and the value
    print(it.first) # Not working
    print(it.second) # Not working
    it ++ # Not working

This does not compile: Object of type 'iterator' has no attribute 'first'

I used map container in cpp before but for this code, I am trying to stick to cython/python, is it possible here?.

Resolved by DavidW Here is an working version of the code, following DavidW answer:

import cython
cimport cython
from licpp.map import map as mapcpp
from cython.operator import dereference, postincrement

def it_through_map(dict mymap_of_int_int):
  # python dict to map
  cdef mapcpp[int,int] mymap_in = mymap_of_int_int
  cdef mapcpp[int,int].iterator it = mymap_in.begin()

  while(it != mymap.end()):
    # let's pretend here I just want to print the key and the value
    print(dereference(it).first) # print the key        
    print(dereference(it).second) # print the associated value
    postincrement(it) # Increment the iterator to the net element

Answer 1

The map iterator doesn't have elements first and second. Instead it has a operator* which returns a pair reference. In C++ you can use it->first to do this in one go, but that syntax doesn't work in Cython (and it isn't intelligent enough to decide to use -> instead of . itself in this case).

Instead you use cython.operator.dereference:

from cython.operator cimport dereference

# ...

print(dereference(it).first)

Similarly, it++ can be done with cython.operator.postincrement