Does the python standard library have function to convert CamelCase to camel_case?

Question

Example:

>>> convert('CamelCase')
camel_case

Answer 1

Not in the standard library, but I found this script that appears to contain the functionality you need.

Answer 2

For the fun of it:

>>> def un_camel(input):
...     output = [input[0].lower()]
...     for c in input[1:]:
...             if c in ('ABCDEFGHIJKLMNOPQRSTUVWXYZ'):
...                     output.append('_')
...                     output.append(c.lower())
...             else:
...                     output.append(c)
...     return str.join('', output)
...
>>> un_camel("camel_case")
'camel_case'
>>> un_camel("CamelCase")
'camel_case'

Or, more for the fun of it:

>>> un_camel = lambda i: i[0].lower() + str.join('', ("_" + c.lower() if c in "ABCDEFGHIJKLMNOPQRSTUVWXYZ" else c for c in i[1:]))
>>> un_camel("camel_case")
'camel_case'
>>> un_camel("CamelCase")
'camel_case'

Answer 3

''.join('_'+c.lower() if c.isupper() else c for c in "DeathToCamelCase").strip('_')
re.sub("(.)([A-Z])", r'\1_\2', 'DeathToCamelCase').lower()

Answer 4

A horrendous example using regular expressions (you could easily clean this up :) ):

def f(s):
    return s.group(1).lower() + "_" + s.group(2).lower()

p = re.compile("([A-Z]+[a-z]+)([A-Z]?)")
print p.sub(f, "CamelCase")
print p.sub(f, "getHTTPResponseCode")

Works for getHTTPResponseCode though!

Alternatively, using lambda:

p = re.compile("([A-Z]+[a-z]+)([A-Z]?)")
print p.sub(lambda x: x.group(1).lower() + "_" + x.group(2).lower(), "CamelCase")
print p.sub(lambda x: x.group(1).lower() + "_" + x.group(2).lower(), "getHTTPResponseCode")

EDIT: It should also be pretty easy to see that there's room for improvement for cases like "Test", because the underscore is unconditionally inserted.

Answer 5

Here's my solution:

def un_camel(text):
    """ Converts a CamelCase name into an under_score name. 

        >>> un_camel('CamelCase')
        'camel_case'
        >>> un_camel('getHTTPResponseCode')
        'get_http_response_code'
    """
    result = []
    pos = 0
    while pos < len(text):
        if text[pos].isupper():
            if pos-1 > 0 and text[pos-1].islower() or pos-1 > 0 and \
            pos+1 < len(text) and text[pos+1].islower():
                result.append("_%s" % text[pos].lower())
            else:
                result.append(text[pos].lower())
        else:
            result.append(text[pos])
        pos += 1
    return "".join(result)

It supports those corner cases discussed in the comments. For instance, it'll convert getHTTPResponseCode to get_http_response_code like it should.

Answer 6

This is pretty thorough:

def convert(name):
    s1 = re.sub('(.)([A-Z][a-z]+)', r'\1_\2', name)
    return re.sub('([a-z0-9])([A-Z])', r'\1_\2', s1).lower()

Works with all these (and doesn't harm already-un-cameled versions):

>>> convert('CamelCase')
'camel_case'
>>> convert('CamelCamelCase')
'camel_camel_case'
>>> convert('Camel2Camel2Case')
'camel2_camel2_case'
>>> convert('getHTTPResponseCode')
'get_http_response_code'
>>> convert('get2HTTPResponseCode')
'get2_http_response_code'
>>> convert('HTTPResponseCode')
'http_response_code'
>>> convert('HTTPResponseCodeXYZ')
'http_response_code_xyz'

Or if you're going to call it a zillion times, you can pre-compile the regexes:

first_cap_re = re.compile('(.)([A-Z][a-z]+)')
all_cap_re = re.compile('([a-z0-9])([A-Z])')
def convert(name):
    s1 = first_cap_re.sub(r'\1_\2', name)
    return all_cap_re.sub(r'\1_\2', s1).lower()