fig.append_trace(trace1, 1, 1)
fig.append_trace(trace2, 2, 1)

totalPlot = 2
x = ['trace%s'%(item + 1) for item in range(totalPlot)]
y = [(item + 1) for item in range(totalPlot)]
z = totalPlot * [1]

for i, j, k in zip(x, y, z):
    fig.append_trace(i, j, k)

from plotly import tools
import plotly.plotly as py
import plotly.graph_objs as go

trace1 = go.Scatter(
    x=[1, 2, 3],
    y=[4, 5, 6]
)
trace2 = go.Scatter(
    x=[20, 30, 40],
    y=[50, 60, 70],
)

fig = tools.make_subplots(rows=2, cols=1)


# ----- Loop here ------- START
fig.append_trace(trace1, 1, 1)
fig.append_trace(trace2, 2, 1)
# ----- Loop here ------- END

fig['layout'].update(height=600, width=600, title='i <3 subplots')
py.iplot(fig, filename='make-subplots')