Behavior of matplotlib inline plots in Jupyter notebook based on the cell content

问题

I am curious to understand the below explained behavior of inline matplotlib plots in the Jupyter notebook. I will show three cases:

Case 1: Importing and plotting in separate cells. In this case, the plot appears after executing both the cells once consecutively.

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Case 2: Importing and plotting in the same cell. In this case, the plot doesn't appear when the cell [1] is executed once (no figure in the image below). The plot however appears when the same cell [1] is executed again. This is the issue asked as the question below.

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Case 3: Adding %matplotlib inline to Case 2, all in one cell. In this case, as expected, the plot appears after executing the cell once. So no issues here at all.

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Question

Similar post has been asked here before which only mentioned Cases 2 and 3. The comment by ImportanceOfBeingErnest on the linked post clarified that the Jupyter might be configured in a way to use %matplotlib inline by default.

So my question is not why Cases 1 and 2 work without %matplotlib inline, rather I would like to understand

• Why the cell [1] in Case 2 needs to be executed twice to show the plot while the cells [1] and [2] in Case 1 works when executed only once? Is import matplotlib.pyplot as plt invoking/activating the backend differently under the hood when called in different cells?

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System specs

import sys
print (sys.version)
# 3.6.5 |Anaconda, Inc.

import matplotlib
print (matplotlib.__version__)
# 2.2.2

! jupyter notebook --version
# 5.5.0

来源：https://stackoverflow.com/questions/54329901/behavior-of-matplotlib-inline-plots-in-jupyter-notebook-based-on-the-cell-conten