Difference between revisions of "Python/C3/Parsing-data/English"

Containing title, name of the production team along with the logo of MHRD

Learning objectives

1. Split a string using a delimiter.
2. Remove the whitespace around the string.
3. Convert the datatypes of variables from one type to other.

Pre-requisite slide

ipython

There is an input file containing huge no. of records. Each record corresponds to a student.

'Data set'

Our job is to calculate the arithmetic mean of all the maths marks in the region "B".

We can clearly see that the problem involves reading files and tokenizing.

line = "parse this           string"

record.split(';')

In short, split splits on whitespace if called without an argument and splits on the given argument if it is called with an argument.

Pause the video here, try out the following exercise and resume the video

Assignment 1

splitting without an argument ?

record.split()

Solution 1

This is possible by using the strip method of strings. Let us define a string by typing

unstripped.strip()

Pause the video here, try out the following exercise and resume the video

Assignment 2

a_str = "         white      space            "
a_str.strip()

The splitting and stripping operations are done on a string and their result is also a string. Hence the marks that we have, are still strings and mathematical operations are not possible on them. We must convert them into numbers (integers or floats), before we can perform mathematical operations on them.

mark = int(float(mark_str))
type(mark_str)
type(mark)

Pause the video here, try out the following exercise and resume the video

Assignment 3

int("1.25")

flt = float(dcml_str)
flt
number = int(flt)
number

Now that we have all the machinery required to parse the file, let us solve the problem. We first read the file line by line and parse each record. We then see if the region code is B and store the marks accordingly.

for line in open("/home/fossee/sslc.txt"):
    fields = line.split(";")

    region_code = fields[0]
    region_code_stripped = region_code.strip()

    math_mark_str = fields[5]
    math_mark = float(math_mark_str)

    if region_code == "B":
        math_marks_B.append(math_mark)

math_marks_mean

Summary slide

1. Tokenize a string using various delimiters like semi-colons.
2. Split a data separated by delimiters by using the function split().
3. Get rid of extra white spaces around using the strip() function.
4. Convert datatypes of numbers from one type to another.
5. Parse input data and perform computations on it.

Self assessment questions slide

1. How do you split the string "Guido;Rossum;Python" to get the words.
2. How will you remove the extra whitespace in this sentence " Hello World "
3. What does int("20.0") produce

• • 20
  • 20.0
  • Error
  • "20"

Solution of self assessment questions on slide

1. We can split the string the semi-colons by passing it as an argument to the split function as line.split(';')
2. " Hello World ".strip() will remove the extra whitespaces around the string.
3. int("20.0") will give an error, because converting a float string, 20.0, directly into integer is not possible.

Acknowledgment slide