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

# # Simple IO
# <hr style="border-top-width: 4px; border-top-color: #34609b;">
# This simple ROOTbook shows how to create a [histogram](https://root.cern.ch/doc/master/classTH1F.html), [fill it](https://root.cern.ch/doc/master/classTH1.html#a77e71290a82517d317ea8d05e96b6c4a) and [write it](https://root.cern.ch/doc/master/classTObject.html#a19782a4717dbfd4857ccd9ffa68aa06d).

# In[1]:


import ROOT


# In[2]:


get_ipython().run_line_magic('jsroot', 'on')


# We now define a function that will create a histogram, fill it and write it to a file. Later, we will read back the histogram from disk.

# In[5]:


def writeHisto(outputFileName):
    outputFile = ROOT.TFile(outputFileName, "RECREATE")
    h = ROOT.TH1F("theHisto","My Test Histogram;X Title; Y Title",64, -4, 4)
    h.FillRandom("gaus")
    # now we write to the file
    h.Write()


# All objects the class of which has a dictionary can be written on disk. By default, the most widely used ROOT classes are shipped with a dictionary: the histogram is one of those.
# Writing on a file is as simple as invoking the [*Write* method](https://root.cern.ch/doc/master/classTObject.html#a19782a4717dbfd4857ccd9ffa68aa06d).
# 
# Now we invoke the function:

# In[6]:


writeHisto("output.root")


# Before reading the object, we can check from the commandline the content of the file with the [**rootls** utility](https://root.cern.ch/how/how-quickly-inspect-content-file):

# In[8]:


get_ipython().run_cell_magic('bash', '', 'rootls -l output.root\n')


# We see that the file contains one object of type TH1F, the name of which is *theHisto* and the title of which is *My Test Histogram*. 
# 
# Let's now use the ROOT interface to read it and draw it:

# In[10]:


inputFile = ROOT.TFile("output.root")
h = inputFile.theHisto
c = ROOT.TCanvas()
h.Draw()
c.Draw()


# And that's it!