merge python named tuples

00_named_tuple_merge.py

#
#  I was given about 10 minutes to figure out an exercise that
#  boiled down to merging named tuples
# 
#  Weird thing to expect someone to know.  Certainly anyone who knows this
#  off the top of their head knows a lot about Python.   But not everyone
#  good developer will know this little corner of Python.
#
#  It took me some time inspecting tuples to come up with this approach, slowed
#  by my discomfort with relying on single-underscore members of library objects
#
#  Needless to say I way overshot on time.
#
#  The solution here seems kinda dicey - I don't like relying on
#  single-underscore members of objects, but it works.
# 
#  Important to note that the parameters are positional.
#  So for
#
#      C = namedtuple( 'C', a._fields + b._fields  )
#
#  you probably wouldn't want the results of
#
#      c = C( *b, *a )
#
#  A twist to consider is the case where A and B both have a field
#  of the same name.
#
from collections import namedtuple

A = namedtuple( 'A', ['a1', 'a2'] )
B = namedtuple( 'B', ['b1', 'b2'] )
C = namedtuple( 'C',  A._fields + B._fields )

a = A( 'aaa1', 'aaa2' )
b = B( 'bbb1', 'bbb2' )
c = C( *a, *b )

print( c )

# => C(b1='aaa1', b2='aaa2', a1='bbb1', a2='bbb2')

01_merge_objects-to-named-tuple.py

#!/usr/bin/env python3
"""
Merge multiple objects into a single named tuple
"""

from collections import namedtuple
from functools import reduce


def reducer( accum, d ):
   accum.update(d)
   return accum

def  tuplemerge( *dictionaries ):
   merged = reduce( reducer, dictionaries, {} )
   return namedtuple('Merged', merged )(**merged) # <==== Gist of the gist

if __name__ == '__main__':
    obj1 = { 'a': 1, 'b': 2, 'c': 3 }
    obj2 = { 'd': 44, 'e': 55, 'f': 66 }
    obj3 = { 'g': 88, 'h': 99, 'f': 111 } # <=== this 'f' overrides previous 'f'
    print(tuplemerge( obj1,obj2,obj3 ))
    
    # => Merged(a=1, b=2, c=3, d=44, e=55, f=111, g=88, h=99)

Thank you for this post. I was also asked this question during an interview, and I had a very similar experience. I also had a very limited amount of time (< 15 minutes) to develop a solution. I felt it was a language specific question, as this places a major emphasis on one's knowledge of python and python syntax

Same spot - really regret trying to play with namedtuples that I am not very familiar with. But I remember just converting them dicts. It took no more than couple of minutes to do this

from collections import namedtuple

A = namedtuple( 'A', ['a1', 'a2'] )
B = namedtuple( 'B', ['b1', 'b2'] )
C = namedtuple( 'C', ['a1', 'c2'] )

a = A( 'aa1', 'aa2' )
b = B( 'bb1', 'bb2' )
c = C( 'cc1', 'cc2' )

def merge(ntuples):
    m = {}
    for i in ntuples:
        m.update(i._asdict())
    M = namedtuple("M", m.keys())(*m.values())
    return M
    
print(merge([a,b,c]))