====== Computer Lab 04, Iterables ======
more complex data types: Strings, tuples, lists. Traversing. Basic methods.

===== puzzle =====
  * a weekly puzzle to train the brain

===== practical work =====
implement the following functions and test them appropriately.

==== strings ====


<code python>
def count_chars(string, char):
    """Return the number of occurances of char in string.
    
    :param string: a string. Example "hello world"
    :param char: character. Example "l"
    :return: int number of char occurences in string
    >>> count_chars("hello","l")
    2
    """
</code>

<code python>
def replace_chars(string, char_original, char_replacement):
    """Return a new string with all occurences of char_original replaced by char_replacement.
    
    :param string: string in which some chars shall be replaced
    :param char_original: character to be replaced
    :param char_replacement: character to be inserted instead of char_original
    :return: a new string with replaced characters
    >>> replace_chars("hello","h","H")
    "Hello"
    """
</code>

<code python>
def reverse_string(string):
    """Return a reversed version of string.

    :param string: string to be reversed
    :return: reversed string
    >>> reverse_string("hello")
    "olleh"
    """
</code>

<code python>
def is_palindrom(string):
    """Return True if and only if the string is equal to its reversed version.
    
    :param string: string to check for palindrom
    :return: boolean
    >>> is_palindrom("aka")
    True
    >>> is_palindrom("hello")
    False
    """
</code>

==== lists ====

<code python>
def remove_duplicates(items):
    """Remove duplicate items.
    
    :param items: input list, can contain anything
    :return: (unique_list, duplicates)
        unique_list - a list with unique items only
        duplicates - a list with items that were in items more than once
    >>> remove_duplicates(['h','e','l','l','o'])
    (['h','e','l','o'],['l'])
    """
</code>

===== homework =====
  * Solve homework [[courses:be5b33prg:homeworks:quadratic_equation|]] and submit it via Upload system in time! Check the deadline in Upload system.
  * The homework from last week was to read chapters 6,7,8,9 from {[a4b99rph:Wentworth2012]}. Go through them once more and concentrate on things you do not understand.
  * Read chapter 11 (Lists) from {[a4b99rph:Wentworth2012]}.