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

# # Running Code

# First and foremost, the IPython Notebook is an interactive environment for writing and running code. IPython is capable of running code in a wide range of languages. However, this notebook, and the default kernel in IPython 2.0, runs Python code.

# ## Code cells allow you to enter and run Python code

# Run a code cell using `Shift-Enter` or pressing the <button class='btn btn-default btn-xs'><i class="icon-play fa fa-play"></i></button> button in the toolbar above:

# In[3]:


a = 10


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print(a)


# There are two other keyboard shortcuts for running code:
# 
# * `Alt-Enter` runs the current cell and inserts a new one below.
# * `Ctrl-Enter` run the current cell and enters command mode.

# ## Managing the IPython Kernel

# Code is run in a separate process called the IPython Kernel.  The Kernel can be interrupted or restarted.  Try running the following cell and then hit the <button class='btn btn-default btn-xs'><i class='icon-stop fa fa-stop'></i></button> button in the toolbar above.

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import time
time.sleep(10)


# If the Kernel dies you will be prompted to restart it. Here we call the low-level system libc.time routine with the wrong argument via
# ctypes to segfault the Python interpreter:

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import sys
from ctypes import CDLL
# This will crash a Linux or Mac system
# equivalent calls can be made on Windows
dll = 'dylib' if sys.platform == 'darwin' else 'so.6'
libc = CDLL("libc.%s" % dll) 
libc.time(-1)  # BOOM!!


# ## Cell menu

# The "Cell" menu has a number of menu items for running code in different ways. These includes:
# 
# * Run and Select Below
# * Run and Insert Below
# * Run All
# * Run All Above
# * Run All Below

# ## Restarting the kernels

# The kernel maintains the state of a notebook's computations. You can reset this state by restarting the kernel. This is done by clicking on the <button class='btn btn-default btn-xs'><i class='fa fa-repeat icon-repeat'></i></button> in the toolbar above.

# ## sys.stdout and sys.stderr

# The stdout and stderr streams are displayed as text in the output area.

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print("hi, stdout")


# In[3]:


from __future__ import print_function
print('hi, stderr', file=sys.stderr)


# ## Output is asynchronous

# All output is displayed asynchronously as it is generated in the Kernel. If you execute the next cell, you will see the output one piece at a time, not all at the end.

# In[4]:


import time, sys
for i in range(8):
    print(i)
    time.sleep(0.5)


# ## Large outputs

# To better handle large outputs, the output area can be collapsed. Run the following cell and then single- or double- click on the active area to the left of the output:

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for i in range(50):
    print(i)


# Beyond a certain point, output will scroll automatically:

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for i in range(500):
    print(2**i - 1)


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