Python Search for Pattern in list of string elements - python-3.x

Question

I'm searching for a pattern in a list of string elements.
As far my code is working fine, but some data is unable to produce required result.
Code
ss = '''
X A
B A
A C
A D
E A
A F
'''.strip()
lst = []
for r in ss.split('\n'):
lst.append(r.split())
paths = []
for e in lst:
# each row in source data
pnew = [] # new path
for p in paths:
if e[0] in p: # if start in existing path
if p.index(e[0]) == len(p)-1: # if end of path
p.append(e[1]) # add to path
else:
pnew.append(p[:p.index(e[0])+1]+[e[1]]) # copy path then add
break
else: # loop completed, not found
paths.append(list(e)) # create new path
if len(pnew): # copied path
paths.extend(pnew) # add copied path
print('\n'.join([' -> '.join(e) for e in paths]))
what i'm getting is
X -> A -> C
B -> A
X -> A -> D
E -> A
X -> A -> F
what my requried result is
B -> A -> C
X -> A -> D
E -> A -> F
X -> A -> C
B -> A -> D
B -> A -> F
X -> A- > F
Based on Cr & Dr I'm Trying to get the pattern (Cr & Dr are optional)
X A Cr
B A Cr
A C Dr
A D Dr
E A Cr
A F Dr

Answer 1

It's easier to handle this with pandas:
import pandas as pd
from io import StringIO
ss = '''
X A
B A
A C
A D
E A
A F
'''.strip()
df = pd.read_csv(StringIO(ss), sep=' ', names=['source', 'target'])
df = df.merge(df, how='inner', left_on='target', right_on='source')
df = df[['source_x', 'target_x', 'target_y']]
df.apply(lambda x: ' -> '.join(x), axis=1).sort_values()