Why do I get a runtime error with inbuilt function vs separate function python?

• I get a runtime error with this code:

``````class Solution(object):
def wallsAndGates(self, rooms):
"""
:type rooms: List[List[int]]
:rtype: void Do not return anything, modify rooms in-place instead.
"""
def dfs(i,j,d):
for I,J in (i-1,j),(i+1,j),(i,j-1),(i,j+1):
if 0<=I<len(rooms) and 0<=J<len(rooms[0]) and d+1<rooms[I][J]:
rooms[I][J]=d+1
dfs(I,J,d+1)
if not rooms: return
m,n=len(rooms), len(rooms[0])
for i in xrange(m):
for j in xrange(n):
if not rooms[i][j]:
dfs(i,j,0)
``````

However, I do not get a runtime error with this (the only difference is the definition is moved outside)

``````class Solution(object):
def wallsAndGates(self, rooms):
"""
:type rooms: List[List[int]]
:rtype: void Do not return anything, modify rooms in-place instead.
"""

for i in xrange(len(rooms)):
for j in xrange(len(rooms[0])):
if rooms[i][j]==0: self.dfs(rooms,i,j)

def dfs(self,rooms,i,j):
for I,J in (i-1,j),(i+1,j),(i,j-1),(i,j+1):
if 0<=I<len(rooms) and 0<=J<len(rooms[0]) and rooms[i][j]+1<rooms[I][J]:
rooms[I][J]=rooms[i][j]+1
self.dfs(rooms,I,J)``````

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