'''
Write a function that takes a DNA sequence (a string of characters A, T, C, G) 
and returns a dictionary with the counts of each nucleotide.

Handle invalid characters by ignoring them.

Provide an option to return the counts as a percentage of the total number of
nucleotides.

Example outputs:

dna_count("ATCGATCGAATCGA")  
# Returns {'A': 5, 'T': 3, 'C': 4, 'G': 3}

dna_count("ATCGATCGAATCGA", percent=True)  
# Returns {'A': 0.357, 'T': 0.214, 'C': 0.286, 'G': 0.214}
'''

# Your code here