This file has a particular structure. Each line in the file is a set of 11 fields:

The following are the fields in any given line.

* Pass/Fail - This field is blank here because the particular candidate was absent for an exam if not it would've been one of (P/F)

* Withheld - Again blank in this case(W)

Let us now look at the problem we wish to solve:

Draw a pie chart representing the proportion of students who scored more than 90% in each region in Science.

This is the result we expect:

#slide of result.

In order to solve this problem, we need the following machinery:

File Reading - which we have already looked at.

parsing  - which we have looked at partially.

Dictionaries - we shall be introducing the concept of dictionaries here.

And finally plotting - which we have been doing all along.

Let's first start off with dictionaries.

We earlier used lists briefly. Back then we just created lists and appended items into them. 

In order to access any element in a list, we use its index number. Index starts from 0.

For eg. x[0] will give 1 and x[3] will 7.

There are times when we can't access things through integer indexes. For example consider a telephone directory, we give it a name and it should return back corresponding number. List is not the best kind of data structure for such problems, and hence Python provides support for dictionaries. Dictionaries are key value pairs. Lists are indexed by integers while dictionaries are indexed by strings. For example:

Please note the values cannot be searched in a dictionaries.

'In a telephone directory one can search for a number based on a name, but not for a name based on a number'

to obtain the list of all keys in a dictionary type

Similarly,

Let's now see what the dictionary contains

d 

As we saw previously we will be dealing with lines with content of the form

Here ';' is delimiter, that is ';' is used to separate the fields.

We shall create one string variable to see how can we process it to get the desired output.

Previously we saw how to split on spaces when we processed the pendulum.txt file. Let us now look at how to split a string into a list of fields based on a delimiter other than space.

Let's now check what 'a' contains.

a

a[0] is the region code, a[1] the roll no., a[2] the name and so on.

Similarly, a[6] will give us the science marks of that particular region.

So we create a dictionary of all the regions with number of students having more than 90 marks.

Let's now start off with the code

now we read the record data one by one from the file sslc1.txt

    we split the record on ';' and store them in a list by: fields equals record.split(';')

    now we get the region code of a particular entry by region_code equal to fields[0].strip.

The strip() is used to remove all leading and trailing white spaces from a given string

    now we check if the region code is already there in dictionary by typing

    Note that this if statement is inside the for loop so for the if block we will have to give additional indentation.

    we again come back to the older 'for' loop indentation and we again strip the string and to get the science marks by

       	  if yes we add 1 to the value of dictionary for that region by

    Hit return twice to exit the for loop

the first argument to the pie function is the values to be plotted. The second is an optional argument which is used to label the regions.

That brings us to the end of this tutorial. We have learnt about dictionaries, some basic string parsing and plotting pie chart in this tutorial. Hope you have enjoyed it. Thank you.