Shortest code for printing line startswith ['a', 'b'] and endswith ['y', 'z'] Python 3

Question

For an assignment I have to print lines from a text that start with "W" and "Z" and end in "n" and "t" (so W-n, W-t, Z-n, Z-t combo's). I have a code now that works, but it seems a bit long and I was wondering if there is a way to shorten it?

This is the code:

import sys

def main():

    for line in sys.stdin:
        line = line.rstrip()
        if line.startswith("W") and line.endswith("n"):
                print(line)
        if line.startswith("W") and line.endswith("t"):
                print(line)
        if line.startswith("Z") and line.endswith("n"):
                print(line)
        if line.startswith("Z") and line.endswith("t"):
                print(line)

main()

As I said, it works, but it seems a bit elaborate. Any tips on how to shorten?

I tried line.startswith("Z","W") and line.endswith("t","n") but I get a Type Error (all slice indices must be integers or None or have an __index__method).

Look up regular expression. It will allow you to find patterns like that in a lot less code. — Kilzrus, Sep 29 '17 at 13:12

user2390182 · Accepted Answer · 2017-09-29T13:13:42.010

6

You could do this:

line = line.rstrip()
if line and line[0] in "WZ" and line[-1] in "nt":
    print(line)

Or use regular expressions:

import re 
# ...
if re.match(r'^[WZ].*[nt]$', line):
    print(line)

# ^ beginning of string
# $ end of string
# [WX] matches W or X
# .*  any character 0 or more times

See the docs on Python regex syntax.

edited Sep 29 '17 at 13:13

answered Sep 29 '17 at 13:07

user2390182

72,016
6
67
89

`re.match` captures only if the match starts at the beginning of the string; the `^` can be removed – Chen A. Sep 29 '17 at 13:15
I actually agree; I use `search` instead of `match` usually and then it's required. – Chen A. Sep 29 '17 at 13:24

score 3 · Answer 2 · answered Sep 29 '17 at 13:11

startswith and endswith also accept a tuple as argument (see doc). So this will work:

line.startswwith(('W', 'Z'))
line.endswith(('t','n'))

Your code could shorten to:

import sys

def main():

    for line in sys.stdin:
        line = line.rstrip()
        if line.startswith(("W", "Z")) and line.endswith(("n", "t")):
                print(line)

main()

Chen A. · Answer 3 · 2017-09-29T13:38:02.140

0

Use regex.

import re

pattern = '[ZW].*[nt]$'

for line in sys.stdin:
    line = line.rstrip()
    mo = re.match(p, line)
    if mo:
        print(line)

Pattern explained:

[ZW] matches one of the two characters; because we use re.match, it matches only if the string begins with the pattern. So it has to start with Z or W
.* matches anything; char, int, space, etc. one or more times
[nt]$ means match n or t (lower case) and $ makes it a match only if the line ends with these values

edited Sep 29 '17 at 13:38

answered Sep 29 '17 at 13:09

Chen A.

10,140
3
42
61

1

Printing `mo.group()` seems a bit perverse. The requirement was to print the line so just `print(line)` should suffice. – Duncan Sep 29 '17 at 13:23
You're right. I copied the code I tested, and forget to change that :-) thanks – Chen A. Sep 29 '17 at 13:25
and the question has the python-3.x tag so print function preferred. – Duncan Sep 29 '17 at 13:31

score 0 · Answer 4 · answered Sep 29 '17 at 13:11

0

or you could use a regex

import re

r = re.compile(r^"[WZ].+[nt]$")

m = r.match('Woot')
m.group()

answered Sep 29 '17 at 13:11

David Jenkins

461
3
8

score 0 · Answer 5 · answered Sep 29 '17 at 13:12

str.startswith allows you to supply a tuple of strings , you have to use a tuple ("Z", "W") not "Z", "W".

import sys
def main():
    for line in sys.stdin:
    line = line.rstrip()
    if line.startswith(("Z","W")) and line.endswith(("t","n")):
       print(line)
main()

Shortest code for printing line startswith ['a', 'b'] and endswith ['y', 'z'] Python 3

5 Answers5