Coverage for local/lib/python2.7/site-packages/sage/misc/flatten.py : 92%

"Flatten nested lists" 

import sys 

def flatten(in_list, ltypes=(list, tuple), max_level=sys.maxsize): 

""" 

Flattens a nested list. 

INPUT: 

- in_list -- a list or tuple 

- ltypes -- optional list of particular types to flatten 

- max_level -- the maximum level to flatten 

OUTPUT: 

a flat list of the entries of in_list 

EXAMPLES:: 

sage: flatten([[1,1],[1],2]) 

[1, 1, 1, 2] 

sage: flatten([[1,2,3], (4,5), [[[1],[2]]]]) 

[1, 2, 3, 4, 5, 1, 2] 

sage: flatten([[1,2,3], (4,5), [[[1],[2]]]],max_level=1) 

[1, 2, 3, 4, 5, [[1], [2]]] 

sage: flatten([[[3],[]]],max_level=0) 

[[[3], []]] 

sage: flatten([[[3],[]]],max_level=1) 

[[3], []] 

sage: flatten([[[3],[]]],max_level=2) 

[3] 

In the following example, the vector isn't flattened because 

it is not given in the ltypes input. :: 

sage: flatten((['Hi',2,vector(QQ,[1,2,3])],(4,5,6))) 

['Hi', 2, (1, 2, 3), 4, 5, 6] 

We give the vector type and then even the vector gets flattened:: 

sage: flatten((['Hi',2,vector(QQ,[1,2,3])], (4,5,6)), ltypes=(list, tuple,sage.modules.vector_rational_dense.Vector_rational_dense)) 

['Hi', 2, 1, 2, 3, 4, 5, 6] 

We flatten a finite field. :: 

sage: flatten(GF(5)) 

[0, 1, 2, 3, 4] 

sage: flatten([GF(5)]) 

[Finite Field of size 5] 

sage: flatten([GF(5)], ltypes = (list, tuple, sage.rings.finite_rings.finite_field_prime_modn.FiniteField_prime_modn)) 

[0, 1, 2, 3, 4] 

Degenerate cases:: 

sage: flatten([[],[]]) 

[] 

sage: flatten([[[]]]) 

[] 

""" 

index = 0 

current_level = 0 

new_list = [x for x in in_list] 

level_list = [0]*len(in_list) 

while index < len(new_list): 

len_v=None 

while isinstance(new_list[index], ltypes) and current_level<max_level: 

v = list(new_list[index]) 

len_v = len(v) 

new_list[index : index + 1] = v 

old_level = level_list[index] 

level_list[index : index + 1] = [0]*len_v 

if len_v != 0: 

current_level += 1 

level_list[index + len_v - 1] = old_level + 1 

else: 

current_level -= old_level 

index -=1 

break 

# If len_v==0, then index points to a previous element, so we 

# don't need to do anything. 

if len_v!=0: 

current_level -= level_list[index] 

index += 1 

return new_list