AWK is a text processing language that makes it easy to "search files for lines [...] that contain certain patterns. When a line matches one of the patterns, awk performs specified actions on that line." (GNU Awk User's Guide) This recipe provides a way to do the same thing in python.
Python, 56 lines
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Copy to clipboard1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 | import re
class AwkUnhandledLine( RuntimeError ):
pass
class Awk:
"""awk-like mapping from patterns to handlers."""
def __init__(self):
# Start without any patterns
self.pats=[]
def add(self,pattern,handler=None):
# Add a pattern and its handler,
# precompiling the pattern
self.pats.append((re.compile(pattern),handler))
def process(self,line):
# Find the first pattern that matches the input,
# and call the handler with the result of the match.
for pat, handler in self.pats:
m = pat.match(line)
if m:
if callable(handler):
return handler(**m.groupdict())
else:
return handler
raise AwkUnhandledLine( line )
class AwkFileInput(Awk):
def __init__(self):
import fileinput
self.fileinput = fileinput
Awk.__init__(self)
def processinput(self):
for line in self.fileinput.input():
try:
self.process(line)
except AwkUnhandledLine, e:
raise AwkUnhandledLine(
"Don't understand line %d of file %s: %s" %
(fileinput.filelineno(),
fileinput.filename(),
line) )
# example:
def handle_thing(name=None,num=0):
if name:
print name, "=", float(num)
else:
print float(num), "has no name"
def example():
a = AwkFileInput()
a.add("^#") # Ignore comments (handler==None)
a.add("^(?P<num>\d+\.\d+)", handle_thing) # Print numbers
a.add("^(?P<name>\w+)\s+(?P<num>\d+)", handle_thing) # Print named numbers
a.processinput()
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This is useful for processing a mini-language for data input.
Tags: text
Error handling incorrect.
should be: