# stringfun.py
# Walker M. White (wmw2)
# October 15, 2015
"""A module of recursive functions on Strings."""
import string # constants to help with string
import sys

# Allow us to go really deep
sys.setrecursionlimit(999999999)

def length(s):
    """Returns: number of characters in s
    
    Parameter: s the string to measure
    Precondition s is a string"""
    assert type(s) == str, str(s) + ' is not a string' # get in the habit
    
    # s is empty
    if s == '':
        return 0
    
    # s has at least one character
    # return (length of s[0]) + (length of s[1:])
    return 1 + length(s[1:])


def num_e(s):
    """Returns: number of 'e's in s
    
    Parameter: s the string to count
    Precondition s is a string"""
    assert type(s) == str, str(s) + ' is not a string' # get in the habit
    
    # s is empty
    if s == '':
        return 0
    
    # s has at least one character
    # return (number of 'e's in s[0]) + (number of 'e's in s[1:])
    if s[0] == 'e':
        first = 1
    else:
        first = 0
    
    return first+num_e(s[1:])


def deblank(s):
    """Returns: s but with blanks removed
    
    Parameter: s the string to edit
    Precondition s is a string"""
    assert type(s) == str, str(s) + ' is not a string' # get in the habit

    # s is empty
    if s == '':
        return s
    
    # Remove first whitespace
    if s[0] in string.whitespace:
        return deblank(s[1:])
    
    # Keep first character, but remove later whitespace
    return s[0] + deblank(s[1:]);


def depunct(s):
    """Returns: s but with everything that is not a letter removed 
    
    Parameter: s the string to edit
    Precondition s is a string"""
    assert type(s) == str, str(s) + ' is not a string' # get in the habit
    
    # s is empty
    if s == '':
        return s

    if not s[0] in string.letters:
        return depunct(s[1:])
    
    return s[0] + depunct(s[1:]);


def reverse(s):
    """Returns: s with its characters in reverse order
    
    Parameter: s the string to reverse
    Precondition s is a string"""
    assert type(s) == str, str(s) + ' is not a string' # get in the habit

    if s == '':
        return s
    
    # s has at least 2 chars 
    return reverse(s[1:]) + s[0]