Python Challenge # 2 = removing characters from a string

I have the code:

theory = """}#)$[]_+(^_@^][]_)*^*+_!{&$##]((](}}{[!$#_{&{){
*_{^}$#!+]{[^&++*#!]*)]%$!{#^&%(%^*}@^+__])_$@_^#[{{})}$*]#%]{}{][@^!@)_[}{())%)
())&#@*[#}+#^}#%!![#&*}^{^(({+#*[!{!}){(!*@!+@[_(*^+*]$]+@+*_##)&a开发者_如何转开发mp;)^(@$^]e@][#&)(
%%{})+^$))[{))}&$(^+{&(#%*@&*(^&{}+!}_!^($}!(}_@@++$)(%}{!{_]%}$!){%^%%@^%&#([+[
_+%){{}(#_}&{&++!@_)(_+}%_#+]&^)+]_[@]+$!+{@}$^!&)#%#^&+$@[+&+{^{*[@]#!{_*[)(#[[
]*!*}}*_(+&%{&#$&+*_]#+#]!&*@}$%)!})@&)*}#(@}!^(]^@}]#&%)![^!$*)&_]^%{{}(!)_&{_{
+[_*+}]$_[#@_^]*^*#@{&%})*{&**}}}!_!+{&^)__)@_#$#%{+)^!{}^@[$+^}&(%%)&!+^_^#}^({
*%]&@{]++}@$$)}#]{)!+@[^)!#[%@^!!"""

#theory = open("temp.txt")

key = "#@!$%+{}[]_-&*()*^@/"
new2 =""

print()
for letter in theory:
    if letter not in key:
        new2 += letter

print(new2)

This is a test piece of code to solve the python challenge #2: http://www.pythonchallenge.com/pc/def/ocr.html

The only trouble is, the code I wrote seems to leaves lots of whitespace but I'm not sure why.

Any ideas on how to remove the unnecessary white? In other words I want the code to return "e" not " e ".

---

The challenge is to find a rare character. You could use collections.Counter for that:

from collections import Counter

c = Counter(theory)
print(c.most_common()[-1])

Output

('e', 1)

The unnecessary whitespace could be removed using .strip():

new2.strip()

Adding '\n' to the key works too.

---

The best would be to use regular expression library, like so

import re
characters = re.findall("[a-zA-Z]", sourcetext)
print ("".join(characters))

In a resulting string you will have ONLY an alphabetic characters.

---

If you look at the distribution of characters (using collections.Counter), you get:

• 6000+ each of )@(]#_%[}!+$&{*^ (which you are correctly excluding from the output)
• 1220 newlines (which you are not excluding from the output)
• 1 each of — no, I'm not going to give away the answer

Just add \n to your key variable to exclude the unwanted newlines. This will leave you with just the rare (i.e., 1 occurrence only) characters you need.

P.S., it's highly inefficient to concatenate strings in a loop. Instead of:

new2 =""

for letter in theory:
    if letter not in key:
        new2 += letter

write:

new2 = ''.join(letter for letter in theory if letter not in key)

---

The theory string contains several newlines. They get printed by your code. You can either get rid of the newline, like this:

theory = "}#)$[]_+(^_@^][]_)*^*+_!{&$##]((](}}{[!$#_{&{){" \
"*_{^}$#!+]{[^&++*#!]*)]%$!{#^&%(%^*}@^+__])_$@_^#[{{})}$*]#%]{}{][@^!@)_[}{())%)" \
"())&#@*[#}+#^}#%!![#&*}^{^(({+#*[!{!}){(!*@!+@[_(*^+*]$]+@+*_##)&)^(@$^]e@][#&)(" \
"%%{})+^$))[{))}&$(^+{&(#%*@&*(^&{}+!}_!^($}!(}_@@++$)(%}{!{_]%}$!){%^%%@^%&#([+[" \
"_+%){{}(#_}&{&++!@_)(_+}%_#+]&^)+]_[@]+$!+{@}$^!&)#%#^&+$@[+&+{^{*[@]#!{_*[)(#[[" \
"]*!*}}*_(+&%{&#$&+*_]#+#]!&*@}$%)!})@&)*}#(@}!^(]^@}]#&%)![^!$*)&_]^%{{}(!)_&{_{" \
"+[_*+}]$_[#@_^]*^*#@{&%})*{&**}}}!_!+{&^)__)@_#$#%{+)^!{}^@[$+^}&(%%)&!+^_^#}^({" \
"*%]&@{]++}@$$)}#]{)!+@[^)!#[%@^!!"

or your can filter them out, like this:

key = "#@!$%+{}[]_-&*()*^@/\n"

Both work fine (yes, I tested).

---

a simpler way to output the answer is to:

print ''.join([ c for c in theory if c not in key])

and in your case you might want to add the newline character to key to also filter it out:

key += "\n"

---

You'd better work in reverse, something like this:

out = []                                                                                                       
for i in theory:                                                                                                 
  a = ord(i)                                                                                                   
  if (a > 96 and a < 122) or (a > 65 and a < 90):                                                              
    out.append(chr(a))                                                                                         

print ''.join(out)

Or better, use a regexp.