Python string template substitution with dict of regex groups?

Question

I'm new to python/programing in general and trying to build a statsd to opentsdb proxy based off prometheus' statsd proxy in go. I'm trying to have a string template like the following:

label_name = "${1}_${2}_${3}_${6}"

Then using the above label = string template format, replace the contents of 1,2,3, and 7 with the re.match.groups of a different string. I thought I could do this with strings Template.safe_substitute and a small for loop to turn the groups into a dictionary:

     ...:         label_match_dict = {}
     ...:         for i in range(len(input_match.groups())):
     ...:             label_match_dict[str(i+1)] = input_match.groups()[i]

Yet I am having trouble because it looks like string.Template() is looking for [_a-z][_a-zA-Z0-9] which will not match my dict of {1: "blue", 2: "green", 3: "red", 4: "yellow"}. Now I'm completely lost and feel like there must be a clean way to do this instead of my garden path.

So say I have a statsd metric like:

connstats_by.vip.nested._Common_Domain.89.44.250.117.conncount:40|g

and a regex string like so:

re.compile('connstats_by\\.vip\\.nested\\.([^.]*)\\.([^.]*)\\.([^.]*)\\.([^.]*)\\.([^.]*)\\.([^\:]*)(?:\:)([^\|]*)(?:\|)([^\n]*)')

Which after the above for loop gives me:

{ 1: "_Primary_Domain",
  2: "192",
  3: "168",
  4: "1",
  5: "117",
  6: "conncount",
  7: "40",
  8: "g" }

I just can't seem to wrap my brain around substituting the members of the template with the members of the dict without a really gross looking nested for loop. I feel like I am going down the wrong path. I am hoping someone here can point me toward a more pythonic direction that I can understand 3 months down the road.

Thanks in advance for any help.

what exactly is your problem

Mauricio Cortazar
– Mauricio Cortazar

2018-05-12 01:10:51 +00:00
Commented May 12, 2018 at 1:10 — Mauricio Cortazar
– Mauricio Cortazar, Commented May 12, 2018 at 1:10

cco · Accepted Answer · 2018-05-12 09:23:23Z

2

Your format string wants a positional list, so this should work:

label_name = "${1}_${2}_${3}_${6}"
metric = "connstats_by.vip.nested._Common_Domain.89.44.250.117.conncount:40|g"
rx = re.compile('connstats_by\\.vip\\.nested\\.([^.]*)\\.([^.]*)\\.([^.]*)\\.([^.]*)\\.([^.]*)\\.([^\:]*)(?:\:)([^\|]*)(?:\|)([^\n]*)')
print(label_name.format(*rx.match(metric).groups()))

Which prints

$89_$44_$250_$40

answered May 12, 2018 at 9:23

cco

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1 Comment

Lookcrabs Over a year ago

Oh snap! Thank you so much that's so much simpler than me doing 3 regex substitutions. Now I just need to remove the dollar sign which is nothing. Thank you so much!

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