使用列表中的值检查字符串中的字母和数字序列（Python）

Question

I'm stuck on searching a string for a particular sequence of numbers and letters. I need to be able to search a string (a car reg numberplate) for the sequence of two letters, two numbers and then three letters . So far, I have this:

if any(letters in carReg for letters in letters): # Good enough
    print("")
    valid+=1
    if any(numbers in carReg for numbers in numbers): # Good enough
        valid+=1

if valid==0:
    print("Invalid license plate.")
elif valid==1:
    print("Does not contain both numbers AND letters")
elif valid==2:
    print("Valid License Plate")

where letters and numbers are just lists:

letters = ["A","B","C","D","E","F","G","H","I","J","K","L","M","N","O","P","Q","R","S","T","U","V","W","X","Y","Z"]
numbers = ["1","2","3","4","5","6","7","8","9","0"]

which are declared at the start of the program.

The code above works, but only if the string entered is composed entirely of letters, or entirely of numbers. It doesn't check for a sequence, as the program needs to do.

Edit : carReg is given by this line:

carReg = input("Please enter your licence plate: ")
carReg = carReg.upper()

Answer 1

reg = "ab11foo"

a,b,c = reg[:2],reg[2:4],reg[4:] # slice string into ll nn lll
# check a is all alpha characters, b is made up of 0123456789 and c is again alpha and length is correct
if all((a.isalpha(), b.isdigit(), c.isalpha(), len(c)== 3)):
       print("Valid reg")
else:
     print("Invalid reg")

You could also use sets and set.issuperset :

letters = {"A","B","C","D","E","F","G","H","I","J","K","L","M","N","O","P","Q","R","S","T","U","V","W","X","Y","Z"}
numbers = {"1","2","3","4","5","6","7","8","9","0"}
a,b,c = reg[:2], reg[2:4],reg[4:]

if all((letters.issuperset(a), numbers.issuperset(b), letters.issuperset(c), len(c)==3 )):
    .....

Answer 2

You test is wrong, since you don't take order and count of letters/digits into account. This sounds like the right work for a regex:

import re

if re.match(r"^[A-Za-z]{2}[0-9]{2}[A-Za-z]{3}$", carReg):
    print("Valid :)")
else:
    print("Invalid :(")

the pattern means "two letters in AZ or az, then 2 digits 0-9 and other 3 letters in AZ or az" and the ^$ part means that the string must have that exact format, with no extra trailing or leading parts.

Answer 3

Use normal if condition:

1. Get User input by raw_input() method.
2. Convert to Upper case by string upper() method.
3. Check length of user input by len() method.
4. Check character sequence according to problem definition.

eg

letters = ["A","B","C","D","E","F","G","H","I","J","K","L","M","N","O","P","Q","R","S","T","U","V","W","X","Y","Z"]
numbers = ["1","2","3","4","5","6","7","8","9","0"]

carReg = raw_input("Please enter your licence plate: ")
carReg = carReg.upper()
if len(carReg)==7:
    if carReg[0] in letters and carReg[1] in letters and carReg[2] in numbers and\
    carReg[3] in numbers and carReg[4] in letters and carReg[5] in letters and\
    carReg[6] in letters:
        print "Valid licence"
    else:
        print "Wrong licence"

else:
    print "Wrong licence"

output:

$ python test.py 
Please enter your licence plate: aa123fgr
Wrong licence
$ python test.py 
Please enter your licence plate: ss12fgr             
Valid licence
$ python test.py 
Please enter your licence plate: adw
Wrong licence
$ python test.py 
Please enter your licence plate: 12asder
Wrong licence