"""

=======

Textbox

=======

The Textbox widget lets users interactively provide text input, including

formulas. In this example, the plot is updated using the `.on_submit` method.

This method triggers the execution of the *submit* function when the

user presses enter in the textbox or leaves the textbox.

Note: The `matplotlib.widgets.TextBox` widget is different from the following

static elements: :doc:`/tutorials/text/annotations` and

:doc:`/gallery/text_labels_and_annotations/placing_text_boxes`.

"""

import numpy as np

import matplotlib.pyplot as plt

from matplotlib.widgets import TextBox

fig, ax = plt.subplots()

fig.subplots_adjust(bottom=0.2)

t = np.arange(-2.0, 2.0, 0.001)

l, = ax.plot(t, np.zeros_like(t), lw=2)

def submit(expression):

"""

Update the plotted function to the new math *expression*.

*expression* is a string using "t" as its independent variable, e.g.

"t ** 3".

"""

ydata = eval(expression)

l.set_ydata(ydata)

ax.relim()

ax.autoscale_view()

plt.draw()

axbox = fig.add_axes([0.1, 0.05, 0.8, 0.075])

text_box = TextBox(axbox, "Evaluate", textalignment="center")

text_box.on_submit(submit)

text_box.set_val("t ** 2") # Trigger `submit` with the initial string.

plt.show()

#############################################################################

#

# .. admonition:: References

#

# The use of the following functions, methods, classes and modules is shown

# in this example:

#

# - `matplotlib.widgets.TextBox`