user2914144 user2914144 - 1 year ago 231
Python Question

Receiving a KeyError: '0_0' for my python program

I'm was working on this question (it's from Leetcode):

"Given an integer matrix, find the length of the longest increasing

From each cell, you can either move to four directions: left, right, up or down.
You may NOT move diagonally or move outside of the
boundary (i.e. wrap-around is not allowed).

Example 1:

nums = [
Return 4.

I keep running into a KeyError specifically:

Traceback (most recent call last):
File "/Users/Desktop/", line 41, in <module>
File "/Users/Desktop/", line 31, in longestIncreasingPath
traverse(x, y, [])
File "/Users/Desktop/", line 5, in traverse
if traverse.traveled[str(x_coor) + "_" + str(y_coor)]:
KeyError: '0_0'

and I'm not sure exactly what I'm doing wrong. I understand it has to do with my dictionary. Please let me know if there is anything else I need to post:

class Solution(object):
def longestIncreasingPath(self, matrix):

def traverse(x_coor, y_coor, build):
key = str(x_coor) + "_" + str(y_coor)
if key in traverse.traveled and traverse.traveled[key]:
if traveled[str(x_coor) + "_" + str(y_coor)]:
elif x_coor < 0 or y_coor < 0 or x_coor >= len(matrix[0]) or y_coor >= len(matrix)-1:
elif len(build) > 0 and matrix[x_coor][y_coor] <= build[-1]:
if len(build) > traverse.count:
traverse.count = len(build)

traveled[str(x_coor) + "_" + str(y_coor)] = true
traverse(x_coor, y_coor-1, build)
traverse(x_coor, y_coor+1, build)
traverse(x_coor+1, y_coor, build)
traverse(x_coor-1, y_coor, build)
del traveled[str(x_coor) + "_" + str(y_coor)]

traverse.count = 0
traverse.traveled = {}

for y in range(0, len(matrix)-1, 1):
for x in range(0, len(matrix[0]), 1):
traverse(x, y, [])

matrix = [
test = Solution()

Answer Source

You are trying to access a key (0_0) that doesn't exist yet in the dictionary.

You have to check beforehand if it exists, I'd suggest the in keyword:

key = str(x_coor) + "_" + str(y_coor)
if key in traverse.traveled and traverse.traveled[key]:
    # ...

See also: Avoiding KeyError Exceptions

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