Difference between revisions of "Python-3.4.3/C2/Parsing-data/English"

Objectives

• Split a string using a delimiter.
• Remove the leading, trailing and all whitespaces in a string and
• Convert between different built-in datatypes

System Specifications

• Ubuntu Linux 16.04 operating system
• Python 3.4.3 and
• IPython 5.1.0

Prerequisite slide

If not, see the relevant Python tutorials on this website.

Parsing Data

• Parsing the data is reading data in text form.
• It is converted into a form which can be used for computations.

split() function

split() function breaks up a larger string into smaller strings using a defined separator.

If no argument is specified, then whitespace is used as default separator.

Syntax is: str dot split inside parentheses argument

split() function

This is called string tokenizing.

Type percentage sign pylab and press Enter.

Highlight whitespaces

Let us define a variable str1 as string data type.

Type, str1 is equal to inside double quotes Welcome to insert some whitespaces, then Python tutorials

We can have any number of whitespaces between to and Python tutorials.

But all the spaces are treated as one space.

Highlight output

Type, str1 dot split open and close parentheses.

As we can see, we get a list of strings.

x = "08-26-2009;08-27-2009;08-29-2009"

Type as shown.

Exercise 1

Try this exercise and then resume the video.

Split x using space as argument.

Is it same as splitting without an argument?

And giving space as argument will split the sentence specifically on single whitespace.

Type b is equal to str1 dot split open and close parentheses.

<<PAUSE>>

strip() function

strip function removes all leading and trailing whitespaces in a string.

unstripped is equal to inside double quotes space Hello world space

After splitting and stripping we get a list of strings with leading and trailing spaces stripped off.

<<PAUSE>>

Type, mark underscore str is equal to inside double quotes 1.25

Note that 1.25 is a string and not a float as it is within double quotes.

Here we are converting string to float.

This tells you the datatype of mark_str i.e. string.

This shows mark is a float datatype.

Now we can perform mathematical operations on them.

Exercise 2

What happens if you type, int inside parentheses inside double quotes 1.25 in the terminal?

Highlight ValueError

We can see a ValueError.

We cannot convert a string to integer directly.

Type dcml underscore str is equal to inside double quotes 1.25.

Here we are converting the string into float as we cannot directly convert it into integer.

We are now converting float into integer.

We got the output as integer.

This is how we should convert strings into floats and integers.

<<PAUSE>>

Let me open the file student underscore record.txt in text editor.

Please download it in your Home directory and use it.

It contains records of students and their marks in the State Secondary Board Examination.

It has 1 lakh 80 thousand lines of record.

We are going to read it and process this data.

• Highlight 'A'
• Highlight 015163
• Highlight JOSEPH RAJ S
• Highlight 083;042;47;00;72
• Highlight 24

Consider a sample record from this file.

The following are the fields in any given line.

• Region Code
• Roll Number
• Name
• Marks of 5 subjects
• Total marks

for line in open("student_record.txt"):

fields = line.split(";")

We have already learnt for loop in earlier tutorial.

The for loop will process the student record and split the fields of each record.

math_mark = float(math_mark_str)

if region_code == "A": math_marks_A.append(math_mark)

Highlight math_marks_A

Now we have all the math marks for region A in the list math underscore marks underscore A.

math_marks_mean = sum(math_marks_A) / len(math_marks_A)

print (math_marks_mean)

Highlight len(math_marks_A)

For this, we just have to sum the math marks and divide by the length.

Note that the length will give the number of students in region ‘A’.

Here the mean value for region A is calculated roughly for 1 lakh 80 thousand records.

This is how we split and read a huge data and perform computations on it.

<<PAUSE>>

Summary slide

In this tutorial, we learnt to,

1. Tokenize a string
2. Split a string separated by delimiters with split() function

Summary slide

1. Remove whitespaces using the strip() function.
2. Convert datatypes of numbers from one type to another
3. Parse input data and perform computations on it.

Evaluation

1. How do you split the string “Guido;Rossum;Python" to get the words?

Evaluation

Solutions

1. line.split inside parantheses inside single quotes comma
2. int inside parantheses inside double quotes 20.0 will give an error, because converting a string directly into integer is not possible.

Forum

Fossee Forum

Textbook Companion

Acknowledgment

http://spoken-tutorial.org

For more details, visit this website.

Thank You

Thanks for watching.