replace regex in file using a dictionary

Tue Apr 5 03:59:02 EDT 2011

Hi,
So i want to replace multiple lines in a text file and I have reasoned
the best way to do this is with a dictionary. I have simplified my
example and broadly I get what I want however I am now printing my
replacement string and part of the original expression. I am guessing
that I will need to use a more complicated expression than I am
currently am to achieve what I want?
my aim is to match the expression before the "=" and replace the
string after the equals...
My failed example...
def replace_keys(text, replacements_dict):
 for key, var in replacements_dict.iteritems():
 replacement = "%s = %s" % (key, var)
 text = text.replace(key, replacement)
 return text
# example of two lines of the file
str = \
"""structcn = 150.0
metfrac0 = 0.85
"""
# replacements
replacement_dict = {"structcn": "999.0", "metfrac0": "0.85"}
new_str = replace_keys(str, replacement_dict)
print str
print
print new_str
which produces...
structcn = 150.0
metfrac0 = 0.85
structcn = 999.0 = 150.0
metfrac0 = 0.85 = 0.85
thanks.