#!/usr/bin/env python
# coding: utf-8

# # Please Stop using Pylab

# [Edit] thanks to [Randy Olson](https://github.com/Carreau/posts/pull/3) for sending me a PR with grammar and spelling corrections.

# TL;DR, Please stop advising people to use the `pylab` flag when using IPython.
# It is harmful. If you want to help IPython, try to avoid retweeting, and
# promoting things that use the `pylab` flag and make the authors aware of the issues.
# 
# Use explicit import, and `%matplotlib inline` magic. It is better (and supports switching between inline/not inline.)
# 
# 
# This was mainly prompted by a day where I came across consecutive issues due to
# the pylab flag, and people happy to discover it.
# 

# ## Pylab, my worst friend

# When IPython 1.0 was released almost 6 months ago, we had quite a few decisions to
# make in less than a week and loads of discussions at the last moment. One of
# those decisions comes and goes often: we want to get rid of this stupid `pylab` flag. If
# you look at our stable (1.0) dev doc and examples there shouldn't be
# a mention of the `pylab` flag anywhere. If there is, we will quickly remove it.
# Why? Because it is harmful, first to us, then to new users, to the Python
# community, and finally to research in general. 

# Do you know about pylab? If you don't, please be extra careful and try to avoid it as much as possible.
# It is like smoking: it looks cool at first, then after a few years you realise you can live without it, 
# but it makes you sick. 
# 
# You think you know what `pylab` does? Really? Take few seconds to think what the `pylab` flag is doing, then read the rest.

# ## What is it supposed to do?

# The `pylab` **package** main purpose was to build a [transition tool](https://wiki.scipy.org/PyLab) 
# from other languages to Python. As it was more and more common and painful to do the same import 
# in IPython every time when only the IPython shell was around, the `--pylab` flag was added. Basically, it did the following:
# 
# ```python
# import numpy
# import matplotlib
# from matplotlib import pylab, mlab, pyplot
# np = numpy
# plt = pyplot
# 
# from IPython.core.pylabtools import figsize, getfigs
# 
# from pylab import *
# from numpy import *
# ```
# 
# Did you get it right the first time without cheating ? Are you able to say what has been imported
# in `from pylab import *` ? in `from numpy import *` ?
# 
# 
# Of course, that is not the only thing it does. But was it your intention to do that the last time you used pylab?

# ### It is irreversible

# Once you activate pylab mode, there is no going back. You cannot unimport
# things. Of course, with the `%pylab` magic you can always restart your kernel,
# but with the flag, all your kernels will start in pylab mode. Are you **sure**
# you will not need a non-pylab kernel?

# ### Unclear

# When using the `pylab` flag, your audience usually has no way of knowing that you
# used the flag. If I use `plot(range(10))`, what will happen? Will it pop up a
# figure ? Inline it? Or throw an error?
# 

# In[ ]:


plot(range(10))


# Because I'm mean, I won't execute the cell, so that you don't know whether or
# not I'm running in pylab mode or not. You might think it's not a big deal, but
# in teaching and research it is important to communicate exactly what you are doing.

# ### It pollutes the namespace

# In[1]:


len(get_ipython().user_ns.keys())


# In[2]:


get_ipython().run_line_magic('pylab', '')


# IPython 2.0-dev gives some warning, and will tell you wether it clobbers already non-built-in variables in the user namespace.

# In[3]:


len(get_ipython().user_ns.keys())


# Can you really tell me the 948 additional things you now have in your namespace? Not a big deal? Really?

# ### It replaces built-ins

# In[6]:


sum,all


# Both used to be `<function sum>,<function all>` before using pylab, and this **changes the behavior of your programs!**

# For example, it leads to non-pickable object in some cases:
# 
# 
# @treycausey on Twitter
# 
# > @ogrisel @myusuf3 Ah, very curious. It loads fine in IPython but not in an IPython notebook. I must have a namespace collision or something.
# 
# Me:
# > Let me guess: `$ipython notebook --pylab`? But `$ipython` alone?

# ### Other unrelated actions

# IPython developed and added the rich display protocol, so we added `from IPython.display import display` to what `import pylab` does.
# 
# Because matplotlib can work with different event loops, pylab added options to activate qt/gtk/osx/etc. event loops, and with the QtConsole and Notebook creation, the ability to select the inline backend, which registers display hooks.

# The main things users remember, and often the main message that you can read here and there is that:
# 
# > You need to use Pylab to get inline figures.
# 
# Which is **false**. Inline pylab mode is a convenient method to activate inline, and set up a display hook with matplotlib. You do not need pylab to have inline images, nor do you need matplotlib. 
# With 1.0 and above the recommended way to set up inline figures would be to use `%matplotlib`.
# 

# ### Side Effects

# The worst part is it has the side effect of making people use `pylab` without even knowing it. Later on, they start asking question about how to reuse a graph in matplotlib because no one ever encounters the following code any more:
# 
# ```
# fig,ax = subplots(1,1)
# ax.plot(...)
# ```
# 
# or why their script suddenly does not work in plain Python but works in IPython.
# 

# ### It kills kittens, with a spoon...

# Maybe not kittens, but it will force developers to explain the same things, again, and again, and again...

# In[8]:


from IPython.display import YouTubeVideo
YouTubeVideo('9VDvgL58h_Y',start=4*60+27)


# ## Make `--pylab` disappear.

# Of course, we will not remove the `--pylab` flag for compatibility reasons, but please, for 2014, make the following resolutions:
# 
#  - Use `%matplotlib [inline|qt|osx|gtx]` to select the right backend/event hook.
#  - Use explicit imports
#  - Make people aware of the issues
#  - Help by making no new articles/tutorials that mention `--pylab`
#  
# If really you only [have 10 seconds left](https://xkcd.com/1168/), the `%pylab` magic is fine.

# As usual, this has been written in an IPython Notebook. You can send me pull request if I made mistakes, or if you have any additional remarks on why you shouldn't use `--pylab`.