Entry

Perl-like variable substitutions in a string

Jun 16th, 2004 22:39
extras, Nathan Wallace, unknown unknown, Hans Nowak, Snippet 111, Glyn Webster

"""
Packages: text.regular_expressions
"""
""" Function `perlsub': Does Perl-like variable substitutions in a 
string.
    Glyn Webster <glyn@ninz.org.nz> 2021-04-26
"""
def perlsub(text, vars, pattern = r'\$(\w+)', fussy = 1):
  """ Does Perl-like variable substitutions in a string.
      text    -- the string
      vars    -- a dictionary of varible name to value, typically 'var
()'
      pattern -- the variable pattern. The variable must be in group 1.
                 Defaults to to Perl's "$name" style.
      fussy   -- if true variables not in 'dict' raise KeyError 
(default)
                 if false variables not in `dict' are left alone
      Note: "perlsub(text, dict, r'%\((\w+)\)s', 1)" == "text % dict"
  """
  if fussy:
    return re.sub(pattern, lambda m, v=vars: str(v[m.group(1)]), text)
  else:
    return re.sub(pattern, lambda m, v=vars: str(v.get(m.group(1)), 
m.group(0)), text)
"""
This is a similar function that allows not only variables
but expressions embedded in the string.
ex. print ev("3 + 4 = <3 + 4>") # will print ==> '3 + 4 = 7'
    import sys
    print ev("First item of sys.path is < sys.path[0] >") 
    print ev("<sys #comment>, <%dir%>, <#234*765+34#>") 
The tag and substitution function can be specified
for less fussy mode and other styles.
ex. print ev("ARGV = ${sys.argv}", "\$(\{)(.*?)\}") # Perl,shell style 
    print ev("ARGV = ${sys.AABBCC}", "\$(\{)(.*?)\}", _evlazy) # No 
error
    print ev("ARGV = ${sys.AABBCC}", "\$(\{)(.*?)\}", _evinfo) # Show 
info
"""
import re, sys
def ev(s, pat="<(\W?)(.*?)\\1>", f=lambda x: str(eval(x.group(2)))):
	return re.sub(pat, f, s)
def _evlazy(x): # replace with "" when the expression fails
	try:	return str(eval(x.group(2)))
	except:	return ""
def _evinfo(x): # Show error info if expression fails
	try:	return str(eval(x.group(2)))
	except:	
		import traceback
		ei = sys.exc_info()
		return "<"+str(traceback.format_exception_only(ei
[0],ei[1])[0]).strip("\n")+">"