months = ['January',
      'February',
      'March',
      'April',
      'May',
      'June',
      'July',
      'August',
      'September',
      'October',
      'November',
      'December']

  def valid_month(month):
     for x in months:
         if x==month.capitalize() :
             print x

valid_month("january")
  valid_month("January")
  valid_month("foo")
  valid_month("")
  valid_month("jaNuary")

def valid_month(month):
    for x in months:
        if x[1:] == month[1:] and x[0].capitalize() == month[0].capitalize():
            print x

In [4]: "January"=="janUAry".capitalize()
Out[4]: True

def valid_month(month):
     if month and month[0].capitalize()+month[1:] in months:
         print(month)
     else:
         print(month,"is not found")

>>> valid_month("january")
january
>>> valid_month("January")
January
>>> valid_month("foo")
foo is not found
>>> valid_month("")
 is not found
>>> valid_month("jaNuary")
jaNuary is not found

any(t.isupper() for t in month[1:])