New module regsub contains sub(), gsub() and split() as in nawk.

string.splitfields(s, '') now returns [s] as split() in nawk.
Added _exit to exported functions of os.

Lib/os.py

@@ -18,6 +18,7 @@
 
 try:
 	from posix import *
+	from posix import _exit
 	name = 'posix'
 	curdir = '.'
 	pardir = '..'

Lib/regsub.py

+# Regular expression subroutines:
+# sub(pat, repl, str): replace first occurrence of pattern in string
+# gsub(pat, repl, str): replace all occurrences of pattern in string
+# split(str, pat): split string using pattern as delimiter
+
+
+import regex
+
+
+# Replace first occurrence of pattern pat in string str by replacement
+# repl.  If the pattern isn't found, the string is returned unchanged.
+# The replacement may contain references \digit to subpatterns and
+# escaped backslashes.  The pattern may be a string or an already
+# compiled pattern.
+
+def sub(pat, repl, str):
+	prog = compile(pat)
+	if prog.search(str) >= 0:
+		regs = prog.regs
+		a, b = regs[0]
+		str = str[:a] + expand(repl, regs, str) + str[b:]
+	return str
+
+
+# Replace all (non-overlapping) occurrences of pattern pat in string
+# str by replacement repl.  The same rules as for sub() apply.
+# Empty matches for the pattern are replaced only when not adjacent to
+# a previous match, so e.g. gsub('', '-', 'abc') returns '-a-b-c-'.
+
+def gsub(pat, repl, str):
+	prog = compile(pat)
+	new = ''
+	start = 0
+	first = 1
+	while prog.search(str, start) >= 0:
+		regs = prog.regs
+		a, b = regs[0]
+		if a == b == start and not first:
+			if start >= len(str) or prog.search(str, start+1) < 0:
+				break
+			regs = prog.regs
+			a, b = regs[0]
+		new = new + str[start:a] + expand(repl, regs, str)
+		start = b
+		first = 0
+	new = new + str[start:]
+	return new
+
+
+# Split string str in fields separated by delimiters matching pattern
+# pat.  Only non-empty matches for the pattern are considered, so e.g.
+# split('abc', '') returns ['abc'].
+
+def split(str, pat):
+	prog = compile(pat)
+	res = []
+	start = next = 0
+	while prog.search(str, next) >= 0:
+		regs = prog.regs
+		a, b = regs[0]
+		if a == b:
+			next = next + 1
+			if next >= len(str):
+				break
+		else:
+			res.append(str[start:a])
+			start = next = b
+	res.append(str[start:])
+	return res
+
+
+# Internal subroutines:
+# compile(pat): compile a pattern, caching already compiled patterns
+# expand(repl, regs, str): expand \digit escapes in replacement string
+
+
+# Manage a cache of compiled regular expressions.
+# If the pattern is a string a compiled version of it is returned.
+# If the pattern has been used before we return an already compiled
+# version from the cache; otherwise we compile it now and save the
+# compiled version in the cache.
+# Instead of a string, a compiled regular expression can also be
+# passed.
+# WARNING: if the pattern syntax is changed, the cache should be
+# flushed!
+
+cache = {}
+
+def compile(pat):
+	if type(pat) <> type(''):
+		return pat		# Assume it is a compiled regex
+	if cache.has_key(pat):
+		prog = cache[pat]	# Get it from the cache
+	else:
+		prog = cache[pat] = regex.compile(pat)
+	return prog
+
+
+# Expand \digit in the replacement.
+# Each occurrence of \digit is replaced by the substring of str
+# indicated by regs[digit].  To include a literal \ in the
+# replacement, double it; other \ escapes are left unchanged (i.e.
+# the \ and the following character are both copied).
+
+def expand(repl, regs, str):
+	if '\\' not in repl:
+		return repl
+	new = ''
+	i = 0
+	while i < len(repl):
+		c = repl[i]; i = i+1
+		if c <> '\\' or i >= len(repl):
+			new = new + c
+		else:
+			c = repl[i]; i = i+1
+			if '0' <= c <= '9':
+				a, b = regs[eval(c)]
+				new = new + str[a:b]
+			elif c == '\\':
+				new = new + c
+			else:
+				new = new + '\\' + c
+	return new
+
+
+# Test program, reads sequences "pat repl str" from stdin.
+# Optional argument specifies pattern used to split lines.
+
+def test():
+	import sys
+	if sys.argv[1:]:
+		delpat = sys.argv[1]
+	else:
+		delpat = '[ \t\n]+'
+	while 1:
+		if sys.stdin.isatty(): sys.stderr.write('--> ')
+		line = sys.stdin.readline()
+		if not line: break
+		if line[-1] == '\n': line = line[:-1]
+		fields = split(line, delpat)
+		if len(fields) <> 3:
+			print 'Sorry, not three fields'
+			print 'split:', `fields`
+			continue
+		[pat, repl, str] = split(line, delpat)
+		print 'sub :', `sub(pat, repl, str)`
+		print 'gsub:', `gsub(pat, repl, str)`

Lib/string.py

@@ -63,13 +63,12 @@ def split(s):
 
 # Split a list into fields separated by a given string
 # NB: splitfields(s, ' ') is NOT the same as split(s)!
-# splitfields(s, '') is illegal
-splitfields_error = 'string.splitfields called with empty separator'
+# splitfields(s, '') returns [s] (in analogy with split() in nawk)
 def splitfields(s, sep):
 	res = []
 	nsep = len(sep)
 	if nsep == 0:
-		raise splitfields_error
+		return [s]
 	ns = len(s)
 	i = j = 0
 	while j+nsep <= ns:

Lib/stringold.py

@@ -63,13 +63,12 @@ def split(s):
 
 # Split a list into fields separated by a given string
 # NB: splitfields(s, ' ') is NOT the same as split(s)!
-# splitfields(s, '') is illegal
-splitfields_error = 'string.splitfields called with empty separator'
+# splitfields(s, '') returns [s] (in analogy with split() in nawk)
 def splitfields(s, sep):
 	res = []
 	nsep = len(sep)
 	if nsep == 0:
-		raise splitfields_error
+		return [s]
 	ns = len(s)
 	i = j = 0
 	while j+nsep <= ns: