flatten a nested sequence: distinguishes lists from strings, etc.

flatten.py

# first, a compact one-liner but limited to 2D sequences (nested just one level):

# obvious, but 
	# "nested_list" refers to the nested list you want to flatten,
	# "row" refers to each list comprising the nested_list
	# "itm" refers to each element comprising each row


def flatten(list2D):
	return [itm for row in list2d for itm in row]
	
	
# explanation: derive the list comprehension above from the loop syntax:
flat_list = []
for row in nested_list:
	for itm in row:
		flat_list.append(itm)

# ie, just copy the loop syntax into the list comprehension:
# "for row in nested list for itm in row"
# then add the antecedent (itm):
# "itm for row in nested list for itm in row"


def flatten_nested_seq(nested_seq, ignore_seq=(str, bytes)):
	"""
	returns: generator w/ all items from nested_seq
	pass in: nested_seq, eg, list
	
	"""
	import collections as CL
	for itm in nested_seq:
		if isinstance(itm, CL.Iterable) and not isinstance(itm, ignore_seq):
			yield from flatten_nested_seq(itm)
		else:
			yield itm