Complete the function/method so that it takes CamelCase string and returns the string in snake_case notation. Lowercase characters can be numbers. If method gets number, it should return string.

Examples:

``` javascript
//  returns test_controller
toUnderscore('TestController');

// returns movies_and_books
toUnderscore('MoviesAndBooks');

// returns app7_test
toUnderscore('App7Test');

// returns "1"
toUnderscore(1);
```

``` coffeescript  
#  returns test_controller
toUnderscore 'TestController'

# returns movies_and_books
toUnderscore 'MoviesAndBooks'

# returns app7_test
toUnderscore 'App7Test'

# returns "1"
toUnderscore 1
```

Difficulty: EASY
Starter code: def to_underscore(string):
	

Solutions:
import re

def to_underscore(string):
	return re.sub('(.)([A-Z])', '\\1_\\2', str(string)).lower()


def to_underscore(string):
	string = str(string)
	camel_case = string[0].lower()
	for c in string[1:]:
		camel_case += '_{}'.format(c.lower()) if c.isupper() else c
	return camel_case


def to_underscore(string):
	return ''.join(('_' + c.lower() if c.isupper() else c for c in str(string))).lstrip('_')


import re

def to_underscore(string):
	return re.sub('(?<=.)(?=[A-Z])', '_', str(string)).lower()


import re

def to_underscore(string):
	try:
		return '_'.join((x.lower() for x in re.findall('[A-Z][^A-Z]*', string)))
	except:
		return str(string)


def to_underscore(string):
	string = str(string)
	new = []
	for s in string:
		if not new:
			new.append(s)
		else:
			if s.isupper():
				new.append('_')
			new.append(s)
	return ''.join(new).lower()


def to_underscore(s):
	if isinstance(s, (int, float)):
		return str(s)
	return ''.join([c if c == c.lower() else '_' + c.lower() for c in s]).strip('_')


def to_underscore(s):
	return ''.join(['_' + c.lower() if c.isupper() else c for c in str(s)]).strip('_')


def to_underscore(xs):
	return ''.join((('_' if i and x.isupper() else '') + x.lower() for (i, x) in enumerate(str(xs))))