Limiting User Input to a Range in Python
In the Code Below You'll See It Asking for a 'Shift' Value. My Problem Is That I Want to Limit the Input to 1 Through 26. for Char in Sentence: If Char in...
In the code below you'll see it asking for a 'shift' value. My problem is that I want to limit the input to 1 through 26.
For char in sentence:
if char in validLetters or char in space: #checks for
newString += char #useable characters
shift = input("Please enter your shift (1 - 26) : ")#choose a shift
resulta = []
for ch in newString:
x = ord(ch) #determines placement in ASCII code
x = x+shift #applies the shift from the Cipher
resulta.append(chr(x if 97 <= x <= 122 else 96+x%122) if ch != \
' ' else ch) # This line finds the character by its ASCII code
How do I do this easily?
5 Answers
Another implementation:
shift = 0
while not int(shift) in range(1,27):
shift = input("Please enter your shift (1 - 26) : ")#choose a shift
Use a while loop to keep asking them for input until you receive something you consider valid:
shift = 0
while 1 > shift or 26 < shift:
try:
# Swap raw_input for input in Python 3.x
shift = int(raw_input("Please enter your shift (1 - 26) : "))
except ValueError:
# Remember, print is a function in 3.x
print "That wasn't an integer :("
You'll also want to have a try-except block around the int() call, in case you get a ValueError (if they type a for example).
Note if you use Python 2.x, you'll want to use raw_input() instead of input(). The latter will attempt to interpret the input as Python code - that can potentially be very bad.
Try something like this
acceptable_values = list(range(1, 27))
if shift in acceptable_values:
#continue with program
else:
#return error and repeat input
Could put in while loop but you should limit user inputs so it doesn't become infinite
while True:
result = raw_input("Enter 1-26:")
if result.isdigit() and 1 <= int(result) <= 26:
break;
print "Error Invalid Input"
#result is now between 1 and 26 (inclusive)
Use an if-condition:
if 1 <= int(shift) <= 26:
#code
else:
#wrong input
Or a while loop with the if-condition:
shift = input("Please enter your shift (1 - 26) : ")
while True:
if 1 <= int(shift) <= 26:
#code
#break or return at the end
shift = input("Try Again, Please enter your shift (1 - 26) : ")
Sarah Jenkins is a veteran tech journalist with over 12 years of experience covering artificial intelligence, mobile innovations, and digital ethics. Her insights have appeared in leading technology publications worldwide.
