My answers to Assignment 2

a2.py

def get_length(dna):
    """ (str) -> int

    Return the length of the DNA sequence dna.

    >>> get_length('ATCGAT')
    6
    >>> get_length('ATCG')
    4
    """
    return len(dna)

def is_longer(dna1, dna2):
    """ (str, str) -> bool

    Return True if and only if DNA sequence dna1 is longer than DNA sequence
    dna2.

    >>> is_longer('ATCG', 'AT')
    True
    >>> is_longer('ATCG', 'ATCGGA')
    False
    """
    return len(dna1) > len(dna2)


def count_nucleotides(dna, nucleotide):
    """ (str, str) -> int

    Return the number of occurrences of nucleotide in the DNA sequence dna.

    >>> count_nucleotides('ATCGGC', 'G')
    2
    >>> count_nucleotides('ATCTA', 'G')
    0
    """
    str1 = dna
    str2 = nucleotide
    return str1.count(str2)
        

def contains_sequence(dna1, dna2):
    """ (str, str) -> bool

    Return True if and only if DNA sequence dna2 occurs in the DNA sequence
    dna1.

    >>> contains_sequence('ATCGGC', 'GG')
    True
    >>> contains_sequence('GGATCC', 'GG')
    True
    >>> contains_sequence('ATCCGG', 'GG')
    True
    >>> contains_sequence('ATCGGC', 'GT')
    False
    """
    if dna2 in dna1:
        return True
    if dna2 not in dna1:
        return False       


def is_valid_sequence(dna):
    ''' (str) -> bool
    
    Return True if and only if the DNA sequence is valid
    (that is, it contains no characters other than 'A', 'T', 'C' and 'G').
    
    >>> is_valid_sequence('ATCG')
    True
    >>> is_valid_sequence('ATCg')
    False
    >>> is_valid_sequence('atcg')
    False
    >>> is_valid_sequence('')
    False
    '''
    val_seq = True
    
    for char in dna:
        if char not in 'ATCG':
            val_seq = False

    return val_seq


def insert_sequence(dna1, dna2, int1):
    ''' (str, str, int) -> str
    
    Return the DNA sequence obtained by inserting the second DNA
    sequence into the first DNA sequence at the given index. 
    (You can assume that the index is valid.)
    
    >>> insert_sequence('CCGG', 'AT', 2)
    'CCATGG'
    '''
    return dna1[:int1] + dna2 + dna1[int1:]


def get_complement(dna):
    ''' (str) -> str
    
    Return the complimentry nucleotide for
    a given nucleotide
    
    >>> get_complement('A')
    'T'
    >>> get_complement('G')
    'C'
    >>> get_complement('T')
    'A'
    >>> get_complement('C')
    'G'
    '''
    if dna == 'A':
        return 'T'
    elif dna == 'G':
        return 'C'
    if dna == 'T':
        return 'A'
    elif dna == 'C':
        return 'G'    


def get_complementary_sequence(dna):
    ''' (str) -> str
    
    Return the DNA sequence that is
    complementary to the given DNA sequence.
    
    >>> get_complementary_sequence('AT')
    'TA'
    >>> get_complementary_sequence('ACGTACG')
    'TGCATGC'
    >>> get_complementary_sequence('ACGTACGACGTACG')
    'TGCATGCTGCATGC'
    '''
    r = ""
    for i in dna:
        r = r + get_complement(i)
    return r

get_complementary_sequence isn't calling get_complement on the 'i' variable to get the complementary nucleotide.

Where does it say I have to use it

It doesn't, but: Return the DNA sequence that is
complementary to the given DNA sequence.

This requires that each character be replaced with its complement, which is what get_complement does (for a single character).

r = ""
for i in comp:
r = i + r
return r

will just reverse the i string.

It should be r = r + get_complement(i)

ooooooooooh ok thanks

Ok fixed up the get_compliment as well, posted the old version earlier.

Hey buddy! Have you done assignment 3! please help :)