I wrote a program that shifts letters in a string and returns a dictionary. It works, unless the letter 'w' is within the string. Does anyone know why this happens? This is my code:
def buildCoder(shift):
import string
impStr = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'
resultDict = {}
lowerValues = dict()
for index, letter in enumerate(string.ascii_lowercase):
lowerValues[letter] = index + 1
upperValues = dict()
for index, letter in enumerate(string.ascii_uppercase):
upperValues[letter] = index + 1
inv_lowerValues = {v:k for k, v in lowerValues.items()}
inv_upperValues = {v:k for k, v in upperValues.items()}
for char in impStr:
if char in string.ascii_lowercase:
value = lowerValues[char]
value += shift
if value <= 25:
resultDict[char] = inv_lowerValues[value]
else:
value = abs(26-value)
resultDict[char] = inv_lowerValues[value]
elif char in string.ascii_uppercase:
value = upperValues[char]
value += shift
if value <= 25:
resultDict[char] = inv_upperValues[value]
else:
value = abs(26-value)
resultDict[char] = inv_upperValues[value]
return resultDict
This is the error I get (if 'w'
is included in impStr
):
KeyError Traceback (most recent call last)
<ipython-input-117-0f4ac72e3c63> in <module>()
----> 1 buildCoder(3)
/var/folders/CV/CVkEwo3TGuu4+2cStWCRyE+++TQ/-Tmp-/tmpMr_sV1.py in buildCoder(shift)
KeyError: 0
I also saw this error:
Traceback (most recent call last):
File "submission.py", line 24, in buildCoder
resultDict[char] = inv_lowerValues[value]
KeyError: 0
*** ERROR: Expected to find a dictionary in the line:
Traceback (most recent call last):
File "submission.py", line 24, in buildCoder
resultDict[char] = inv_lowerValues[value]
KeyError: 0
***
Let's use a bit of introspection on your code:
lowerValues['w'] == 23
inv_lowerValues[23] == 'w'
# presumably shift == 3
for char in impStr: # when char==w
if char in string.ascii_lowercase: # it is
value += shift # 23 + 3 == 26
if values <= 25 # it's not
else:
value = abs(26-value)
# abs( 26 - 26 ) == 0
resultDict[char] = inv_lowerValues[value]
# resultDict['w'] = inv_lowerValues[0]; KeyError
It sounds like you just want to be sure that your shift wraps around the alphabet. That's not abs(26-value)
, that's (value % 25)+1
.
I think, you want to write
value = abs(value-25)
instead of
value = abs(26-value)
otherwise you would get 0 as value.
A more concise version of what you are doing:
import string
def buildCoder(shift):
alpha = string.ascii_lowercase
ALPHA = string.ascii_uppercase
if 0 <= shift < 26:
unshifted_letters = ALPHA + alpha
shifted_letters = ALPHA[shift:] + ALPHA[:shift] + alpha[shift:] + alpha[:shift]
return dict(zip(unshifted_letters, shifted_letters))
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