For Loop on Plotly Python

Question

I am trying to replace

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

with the for loop code

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)

so that it will be more scalable as I add more figures. However, the loop code keeps returning 'TypeError: 'str' object does not support item assignment'. What did I do wrong?

Here is the code similar with the one from Plotly:

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')

Exactly which line is giving you an error? The error 'TypeError: 'str' object does not support item assignment' tends to arise when you try to modify a string object in place (change a character for example.) Strings are immutable, so you can't "change" one but you can make a changed copy. — machine yearning
– machine yearning, Commented Aug 24, 2016 at 4:50
@machine yearning: This line is giving me the TypeError: 'fig.append_trace(i, j, k)' — Fxs7576
– Fxs7576, Commented Aug 24, 2016 at 4:54

machine yearning · Accepted Answer · 2016-08-24 05:14:19Z

2

In this code it looks like trace1 is some kind of array-like data structure:

trace1 = go.Scatter(
    x=[1, 2, 3],
    y=[4, 5, 6]
)

So I imagine that when you call fig.append_trace(trace1, 1, 1) it's adding an element to this array-like structure, the first parameter.

However in your reimplementation, you've turned the trace data into a string:

x = ['trace%s'%(item + 1) for item in range(totalPlot)]
...
for i, j, k in zip(x, y, z):
    fig.append_trace(i, j, k)

Here i is an element of x which is in turn a string like 'trace%s'%(item + 1). But you cannot append an element to a string. Python strings are immutable. So when you call append_trace you naturally get an error here about not being able to do what you want with strings.

answered Aug 24, 2016 at 5:14

machine yearning

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2 Comments

Fxs7576 Over a year ago

I see. I will fix the x and make it an array. Thank you for the explanation. :)

machine yearning Over a year ago

Or rather, x is already an array. What you probably need to do is make sure each element of x is a go.Scatter object, instead of a string.

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