Using dictionary key as a regular expression class

[Terry Reedy]

On 1/22/2010 4:47 PM, Chris Jones wrote:
> I was writing a script that counts occurrences of characters in source code files:
>
> #!/usr/bin/python
> import codecs
> tcounters = {}
> f = codecs.open('/home/gavron/git/screen/src/screen.c', 'r', "utf-8")
> for uline in f:
>    lline = []
>    for char in uline[:-1]:
>      lline += [char]

Same but slower than lline.append(char), however, this loop just 
uselessless copies uline[:1]

>    counters = {}
>    for i in set(lline):
>      counters[i] = lline.count(i)

slow way to do this

>    for c in counters.keys():
>      if c in tcounters:
>        tcounters[c] += counters[c]
>      else:
>        tcounters.update({c: counters[c]})

I do not see the reason for intermediate dict

>    counters = {}

duplicate line

> for c in tcounters.keys():
>    print c, '\t', tcounters[c]

To only count ascii chars, as should be the case for C code,

achars = [0]*63
for c in open('xxx', 'c'):
   try:
     achars[ord(c)-32] += 1
   except IndexError:
     pass

for i,n in enumerate(achars)
   print chr(i), n

or sum subsets as desired.

Terry Jan Reedy