You have wrong indentation and the second line with drawString is causing the overlapping.
from reportlab.lib.units import inch
from reportlab.lib.colors import magenta, red
from reportlab.pdfgen import canvas
lyrics = ['This is first line', 'This is second line', 'This is third line', 'This is the fourth line', 'This is the fifth line']
def textsize(canvas):
canvas.setFont('Times-Roman', 20)
canvas.setFillColor(red)
canvas.drawCentredString(2.75*inch, 2.5*inch, "Font Size examples")
canvas.setFillColor(magenta)
size = 7
y = 2.3 * inch
x = 1.3 * inch
for line in lyrics:
canvas.setFont('Helvetica', size)
canvas.drawString(x, y, '%s points' % size)
print x, y, line
canvas.drawString(x + 2*inch, y, line)
y = y - (size * 1.2)
size = size + 1.5
c = canvas.Canvas('font.pdf')
textsize( c )
c.showPage()
c.save()