# Function for counting occurrences of T.
def countT(seq):
    count = 0
    for ch in seq:
        if ch=="T":
            count = count + 1
    return count

# count the occurrences of A
def countA(seq):
    count = 0
    for ch in seq:
        if ch=="A":
            count += 1
    return count

# count the occurrences of a given nucleotide
def countN(seq, n):
    count = 0
    for ch in seq:
        if ch==n:
            count += 1
    return count

#fast python way to do this
def countNfast(seq, n):
    return seq.count(n)

# Return the reverse complement of a nucleotide sequence.
def revComp(seq):
    compDict = {'A' : 'T',
                'T' : 'A',
                'C' : 'G',
                'G' : 'C'}
    complement = ""
    for nuc in seq:
        cmp = compDict[nuc]
        complement = complement + cmp
    return complement[::-1]

# even better way to get the reverse complement
def revComp2(seq):
    compDict = {'A' : 'T',
                'T' : 'A',
                'C' : 'G',
                'G' : 'C'}
    complement = ""
    for nuc in seq:
        cmp = compDict[nuc]
        complement = cmp + complement
    return complement