Given this template:



In [16]:

    
template = """\
Dynamically expanded example:

    @EXAMPLE@

End of file.
"""

Replace @EXAMPLE@ with the following text, preserving indentation:



In [17]:

    
expansion = """\
def hello():
    print('hellowording..')
hello()
"""

So, the result should look like:



In [18]:

    
test = """\
Dynamically expanded example:

    def hello():
        print('hellowording..')
    hello()

End of file.
"""

Standard string replacement (FAIL)



In [21]:

    
try1 = template.replace('@EXAMPLE@', expansion)
print(try1)
try1 == test









    



Dynamically expanded example:

    def hello():
    print('hellowording..')
hello()


End of file.







    Out[21]:





False

Using string.Template (FAIL)



In [24]:

    
from string import Template
Template.delimiter = '@'



In [33]:

    
converter = Template(template)
converter









    Out[33]:





<string.Template at 0x33c4130>



In [32]:

    
try2 = converter.substitute(EXAMPLE=expansion)
print(try2)









    



Dynamically expanded example:

    @EXAMPLE@

End of file.

Subclasssing



In [35]:

    
class Converter(Template):
    delimiter = '@'
converter2 = Converter(template)
converter2









    Out[35]:





<__main__.Converter at 0x33c4390>



In [36]:

    
converter2.substitute(EXAMPLE=expansion)









    



---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-36-5878bbe91641> in <module>()
----> 1 converter2.substitute(EXAMPLE=expansion)

C:\Python27\lib\string.pyc in substitute(*args, **kws)
    174             raise ValueError('Unrecognized named group in pattern',
    175                              self.pattern)
--> 176         return self.pattern.sub(convert, self.template)
    177 
    178     def safe_substitute(*args, **kws):

C:\Python27\lib\string.pyc in convert(mo)
    171                 return self.delimiter
    172             if mo.group('invalid') is not None:
--> 173                 self._invalid(mo)
    174             raise ValueError('Unrecognized named group in pattern',
    175                              self.pattern)

C:\Python27\lib\string.pyc in _invalid(self, mo)
    144             lineno = len(lines)
    145         raise ValueError('Invalid placeholder in string: line %d, col %d' %
--> 146                          (lineno, colno))
    147 
    148     def substitute(*args, **kws):

ValueError: Invalid placeholder in string: line 3, col 13



In [37]:

    
Converter("Try with single @EXAMPLE delimiter.").substitute(EXAMPLE='at')









    Out[37]:





'Try with single at delimiter.'



In [38]:

    
Converter("Try with double @EXAMPLE@ delimiter.").substitute(EXAMPLE='at')









    



---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-38-5a460037c4cd> in <module>()
----> 1 Converter("Try with double @EXAMPLE@ delimiter.").substitute(EXAMPLE='at')

C:\Python27\lib\string.pyc in substitute(*args, **kws)
    174             raise ValueError('Unrecognized named group in pattern',
    175                              self.pattern)
--> 176         return self.pattern.sub(convert, self.template)
    177 
    178     def safe_substitute(*args, **kws):

C:\Python27\lib\string.pyc in convert(mo)
    171                 return self.delimiter
    172             if mo.group('invalid') is not None:
--> 173                 self._invalid(mo)
    174             raise ValueError('Unrecognized named group in pattern',
    175                              self.pattern)

C:\Python27\lib\string.pyc in _invalid(self, mo)
    144             lineno = len(lines)
    145         raise ValueError('Invalid placeholder in string: line %d, col %d' %
--> 146                          (lineno, colno))
    147 
    148     def substitute(*args, **kws):

ValueError: Invalid placeholder in string: line 1, col 25



In [50]:

    
class DoubleEnded(Template):
    delimiter = '@'
    pattern = r'''
    %(delim)s             # start with @
    (?:                   # non-capturing group
        (?P<escaped>%(delim)s) |       # if next is @, both are escaped @
        (?P<named>%(id)s%(delim)s) |    # if next is id, it should end with @
        (?P<braced>%(id)s%(delim)s) |   # need to have braced in regex too
        (?P<invalid>)                  # catch all for errors
    )
    '''
print DoubleEnded.pattern









    



<_sre.SRE_Pattern object at 0x02640488>



In [51]:

    
DoubleEnded("Try with double @EXAMPLE@ delimiter.").substitute(EXAMPLE='at')









    Out[51]:





'Try with double @EXAMPLE@ delimiter.'

^^^ This doesn't work, because if pattern is defined, delimiter won't work anymore.



In [57]:

    
class DoubleEndedAt(Template):
    pattern = r'''
    %(delim)s             # start with @
    (?:                   # non-capturing group
        (?P<escaped>%(delim)s) |       # if next is @, both are escaped @
        (?P<named>%(id)s)%(delim)s |    # if next is id, it should end with @
        (?P<braced>%(id)s)%(delim)s |   # need to have braced in regex too
        (?P<invalid>)                  # catch all for errors
    )
    ''' % dict(delim='@', id='[_a-z][_a-z0-9]*')



In [58]:

    
DoubleEndedAt("Try with double @EXAMPLE@ delimiter.").substitute(EXAMPLE='at')









    Out[58]:





'Try with double at delimiter.'



In [59]:

    
DoubleEndedAt("Try with single @EXAMPLE delimiter.").substitute(EXAMPLE='at')









    



---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-59-0427b214a63c> in <module>()
----> 1 DoubleEndedAt("Try with single @EXAMPLE delimiter.").substitute(EXAMPLE='at')

C:\Python27\lib\string.pyc in substitute(*args, **kws)
    174             if mo.group('invalid') is not None:
    175                 self._invalid(mo)
--> 176             raise ValueError('Unrecognized named group in pattern',
    177                              self.pattern)
    178         return self.pattern.sub(convert, self.template)

C:\Python27\lib\string.pyc in convert(mo)
    171                 return '%s' % (val,)
    172             if mo.group('escaped') is not None:
--> 173                 return self.delimiter
    174             if mo.group('invalid') is not None:
    175                 self._invalid(mo)

C:\Python27\lib\string.pyc in _invalid(self, mo)
    144         else:
    145             colno = i - len(''.join(lines[:-1]))
--> 146             lineno = len(lines)
    147         raise ValueError('Invalid placeholder in string: line %d, col %d' %
    148                          (lineno, colno))

ValueError: Invalid placeholder in string: line 1, col 17



In [60]:

    
DoubleEndedAt("Try with escaped @@ delimiter.").substitute(EXAMPLE='at')









    Out[60]:





'Try with escaped @ delimiter.'

Finally, the real example.



In [64]:

    
try3 = DoubleEndedAt(template).substitute(EXAMPLE=expansion)
print(try3)
try3 == test









    



Dynamically expanded example:

    def hello():
    print('hellowording..')
hello()


End of file.







    Out[64]:





False

Custom function (SUCCESS)



In [106]:

    
def expand(text, needle, replacement):
    """replace `needle` with replacement preserving indentation"""
    output = []
    repl = replacement.splitlines(True)
    for i, line in enumerate(text.splitlines(True)):
        pos = line.find(needle)
        #print i, repr(pos)
        if pos == -1:
            output.append(line)
        else:
            # add first line of replacement
            outline = [line[0:pos], repl[0]]
            if len(replacement) == 1:
                outline.append(line[pos+len(needle):])
            else:
                # [ ] copy whitespace symbols
                indent = ' '*pos
                for rep in repl[1:]:
                    outline.append(indent)
                    outline.append(rep)
                outline.append(line[pos+len(needle):])
            output.append(''.join(outline))
    return ''.join(output)



In [107]:

    
print expand(template, '@EXAMPLE@', expansion)









    



Dynamically expanded example:

    def hello():
        print('hellowording..')
    hello()


End of file.



In [111]:

    
try4 = expand(template, '@EXAMPLE@', expansion.strip())
print try4
try4 == test









    



Dynamically expanded example:

    def hello():
        print('hellowording..')
    hello()

End of file.







    Out[111]:





True



In [112]:

    
print expand('replace me with something', 'me', 'something')









    



replace something with something



In [ ]: