Python one-liner to standardise input string

Question

I'm trying to standardise the user input in this format: dddL where d is a digit and L a capital letter. If the user doesn't add enough digits, I want to fill the missing digits with leading zeroes, if he adds anything else than at most 3 digits and a letter, just reject:

input/standardised example:

input: '1a'
output: '001A'

input: '0a'
output: '000A'

input: '05c'
output: '005C'

input: '001F'
output: '001F' (unchanged)

input: '10x'
output: '010X'

input: '110x'
output: '110X'

My broken attempt right now returns nothing for some reason: (doesn't yet deal with rejecting invalid input)

 >>> x = ['0a', '05c', '001F', '10x']
 >>> [i.upper() if len(i)==4 else ('0' * j) + i.upper() for j in range(4-len(i)) for i in x]
 []

I'm not looking necessarily for list processing, I only want it to work for a single variable as input

The zero-padding part is answered here: http://stackoverflow.com/questions/339007/nicest-way-to-pad-zeroes-to-string — Peter DeGlopper, Sep 17 '14 at 16:00
Wow, then my accepting solution boils down to `[i.upper().zfill(4) for i in x]` — confused00, Sep 17 '14 at 16:02
Yep. And you can check `re.match(r"\d{3}[A-Z]", i.upper().zfill(4))` to detect cases where you want to reject. — Peter DeGlopper, Sep 17 '14 at 16:05
Nice, thank you. Can you post this as an answer so I can accept it? — confused00, Sep 17 '14 at 16:06

score 1 · Answer 1 · answered Sep 17 '14 at 16:07

1

For zero padding:

i.zfill(4)

Check invalid input:

import re
re.match("\d{1,3}[A-Z]", i)

Put it together:

[i.zfill(4) for i in x if re.match("\d{1,3}[A-Z]", i)]

Compiling the re separately will make the code faster, so:

x = ['0A', '05C', '001F', '10x']
import re
matcher = re.compile("\d{1,3}[A-Z]")
out = [i.zfill(4) for i in x if matcher.match(i)]
out == ['000A', '005C', '001F']

RE disassembly:

Regular expression visualization

Debuggex Demo

answered Sep 17 '14 at 16:07

matsjoyce

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Thanks for the answer. I accepted the other answer cause Peter DeGlopper already gave me the answer in the comments before, but I appreciate the help. – confused00 Sep 17 '14 at 16:14

score 1 · Accepted Answer · answered Sep 17 '14 at 16:08

1

One implementation:

acceptableInput = re.compile(r"\d{3}[A-Z]")
paddedInput = i.upper().zfill(4)
if acceptableInput.match(paddedInput):
    # do something
else:
    # reject

answered Sep 17 '14 at 16:08

Peter DeGlopper

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Python one-liner to standardise input string

2 Answers2