Quick and dirty function to template strings

template_string.py

import re

def resolve(template, context):
    """Quick and dirty template resolver, replacing {{ }} with context's values
    For example, {{foo.bar}} is replaced with foo.bar's value, provided "foo" 
    is variable passed in context.
    
    Args:
        template (str)
            Templated string for which will we substitue in templated values
        context (dict)
            Dictionary containing context to apply to the template
    Returns:
        templated_str (str)
            String `template` but with context interpolated into it.
    
    Ex:
        >>> foo = {'bar': 10, 'baz': 15}
        >>> print resolve("Foo's bar + baz is: {{ foo['bar'] + foo['baz'] }}", locals())
        Foo's bar + baz is: 25
    
    """
    # Regular expression to find token between "{{" and "}}"
    #   Group 1 is the full token (ie: "{{ test }}")
    #   Group 2 is just the part to evaluate (ie: "test")
    pattern = re.compile(ur'({{\s*(.+?)\s*}})', flags=re.M+re.S)
    
    def _resolve_var(match):
        # Get the token's resolution path (ie, "a.bleh")
        (full_token, token_path) = match.groups()
        try:            
            return "%s" % eval(token_path, context)
        except Exception as e:
            raise Exception("Unable to resolve %s:\n\t %s" % 
                            (full_token, e))
    
    return re.sub(pattern, _resolve_var, template)

if __name__ == '__main__':
    test_str = 'templated string'
    class A(object):
        b = 10
        c = 'var c'
        d = {'a': "A.d['a']'s value"}
    a = A()
    great_power = True    
    
    print resolve("""
    This is a test {{test_str}}.
    You can be pretty fancy: {{ a.d['a'] }}
    Even do some quick evaluation if needed: {{ "%s = %d" % (a.c, a.b+10) }}
    But be careful you are {{ " ".join(['executing','python']) }} in here!
    But with great power comes {{ 
        ("great responsability" if great_power  
         else "...actually, don't worry about it :)" )
    }}.
    Finally, here is how to do a litteral {{ '{{' }} and {{ '}'+'}' }} if needed.
    """, locals())