Perl Read Csv File Line by Line

What is a CSV file?

A CSV file is a uncomplicated type of obviously text file which uses a specific structure to arrange tabular data. The standard format of a CSV file is divers by rows and columns data where a newline terminates each row to begin the side by side row, and each column is separated by a comma within the row.

CSV is a mutual format for data interchange as it is compact, unproblematic, and general. Many online services allow their users to consign tabular information from the website into a CSV file. Files of CSV will open into Excel, and nearly all databases take a tool to allow import from CSV files.

In this tutorial, y'all will learn:

• What is a CSV file?
• CSV Sample File
• Python CSV Module
• CSV Module Functions
• How to Read a CSV File in Python
• How to read a CSV file into a Dictionary in Python
• How to write CSV File in Python
• Read CSV File using Pandas
• Write CSV File using Pandas

CSV Sample File

Data in the class of tables is as well called CSV (comma separated values) – literally "comma-separated values." This is a text format intended for the presentation of tabular data. Each line of the file is 1 line of the table. The values of private columns are separated by a separator symbol – a comma (,), a semicolon (;) or another symbol. CSV tin can exist easily read and candy by Python.

Consider the post-obit Table

Table Data

Programming language	Designed past	Appeared	Extension
Python	Guido van Rossum	1991	.py
Coffee	James Gosling	1995	.java
C++	Bjarne Stroustrup	1983	.cpp

You can represent this table in csv equally beneath.

CSV Data

Programming language, Designed by, Appeared, Extension

Python, Guido van Rossum, 1991, .py

Java, James Gosling, 1995, .java

C++, Bjarne Stroustrup,1983,.cpp

As you can run across each row is a new line, and each column is separated with a comma. This is an instance of how a CSV file looks like.

Download CSV Data

Python CSV Module

Python provides a CSV module to handle CSV files. To read/write data, you need to loop through rows of the CSV. You need to use the carve up method to get data from specified columns.

CSV Module Functions

In CSV module documentation you can find following functions:

• csv.field_size_limit – render maximum field size
• csv.get_dialect – become the dialect which is associated with the proper noun
• csv.list_dialects – evidence all registered dialects
• csv.reader – read data from a csv file
• csv.register_dialect – associate dialect with name
• csv.writer – write information to a csv file
• csv.unregister_dialect – delete the dialect associated with the name the dialect registry
• csv.QUOTE_ALL – Quote everything, regardless of type.
• csv.QUOTE_MINIMAL – Quote fields with special characters
• csv.QUOTE_NONNUMERIC – Quote all fields that aren't numbers value
• csv.QUOTE_NONE – Don't quote anything in output

In this tutorial, we are going to focus merely on the reader and writer functions which let you to edit, modify, and dispense the data in a CSV file.

How to Read a CSV File in Python

Below are steps to read CSV file in Python.

Step 1) To read data from CSV files, y'all must use the reader function to generate a reader object.

The reader function is developed to take each row of the file and brand a list of all columns. Then, y'all have to choose the column you desire the variable data for.

It sounds a lot more than intricate than it is. Permit's take a look at this Python code to read CSV file, and we will find out that working with csv file isn't so hard.

#import necessary modules import csv with open up('X:\data.csv','rt')as f:   data = csv.reader(f)   for row in data:         print(row)            

Step 2) When you lot execute the program above, the output will exist:

['Programming language; Designed past; Appeared; Extension'] ['Python; Guido van Rossum; 1991; .py'] ['Java; James Gosling; 1995; .coffee'] ['C++; Bjarne Stroustrup;1983;.cpp']            

How to read a CSV file into a Lexicon in Python

You can also y'all utilise DictReader to read CSV files. The results are interpreted as a lexicon where the header row is the fundamental, and other rows are values.

Consider the following code

#import necessary modules import csv  reader = csv.DictReader(open("file2.csv")) for raw in reader:     print(raw)          

The result of this code is:

OrderedDict([('Programming language', 'Python'), ('Designed by', 'Guido van Rossum'), (' Appeared', ' 1991'), (' Extension', ' .py')]) OrderedDict([('Programming language', 'Java'), ('Designed past', 'James Gosling'), (' Appeared', ' 1995'), (' Extension', ' .java')]) OrderedDict([('Programming linguistic communication', 'C++'), ('Designed by', ' Bjarne Stroustrup'), (' Appeared', ' 1985'), (' Extension', ' .cpp')])

And this way to read data from CSV file is much easier than before method. Nevertheless, this is non isn't the all-time way to read data.

How to write CSV File in Python

Here is how to write a CSV file in Python:

When you take a gear up of data that yous would like to shop in a CSV file you take to utilise writer() part. To iterate the data over the rows(lines), you have to apply the writerow() part.

Consider the following example. We write data into a file "writeData.csv" where the delimiter is an apostrophe.

#import necessary modules import csv  with open up('X:\writeData.csv', mode='w') every bit file:     author = csv.writer(file, delimiter=',', quotechar='"', quoting=csv.QUOTE_MINIMAL)      #way to write to csv file     writer.writerow(['Programming linguistic communication', 'Designed by', 'Appeared', 'Extension'])     writer.writerow(['Python', 'Guido van Rossum', '1991', '.py'])     writer.writerow(['Java', 'James Gosling', '1995', '.coffee'])     writer.writerow(['C++', 'Bjarne Stroustrup', '1985', '.cpp'])            

Result in csv file is:

Programming language, Designed by, Appeared, Extension  Python, Guido van Rossum, 1991, .py Java, James Gosling, 1995, .coffee C++, Bjarne Stroustrup,1983,.cpp

Read CSV File using Pandas

Pandas is an opensource library that allows to you lot import CSV in Python and perform data manipulation. Pandas provide an piece of cake manner to create, manipulate and delete the data.

You lot must install pandas library with command <code>pip install pandas</lawmaking>. In Windows, you volition execute this control in Command Prompt while in Linux in the Terminal.

Reading the CSV into a pandas DataFrame is very quick and easy:

#import necessary modules import pandas result = pandas.read_csv('X:\data.csv') print(result)          

Result of the read CSV Pandas example:

Programming language, Designed by, Appeared, Extension  0    Python, Guido van Rossum, 1991, .py 1    Java, James Gosling, 1995, .java 2    C++, Bjarne Stroustrup,1983,.cpp

Very useful library. In just three lines of code you the same result as earlier. Pandas know that the first line of the CSV contained column names, and information technology will use them automatically.

Write CSV File using Pandas

Writing to CSV file with Pandas is every bit easy equally reading. Here you can convince in it. Showtime you must create DataFrame based on the following Python write to CSV lawmaking.

from pandas import DataFrame C = {'Programming language': ['Python','Java', 'C++'],         'Designed by': ['Guido van Rossum', 'James Gosling', 'Bjarne Stroustrup'],         'Appeared': ['1991', '1995', '1985'],         'Extension': ['.py', '.java', '.cpp'],     } df = DataFrame(C, columns= ['Programming language', 'Designed by', 'Appeared', 'Extension']) export_csv = df.to_csv (r'X:\pandaresult.csv', index = None, header=Truthful) # here yous accept to write path, where event file volition be stored impress (df)          

Here is the output

Programming language, Designed by, Appeared, Extension 0    Python, Guido van Rossum, 1991, .py 1    Java, James Gosling, 1995, .java 2    C++, Bjarne Stroustrup,1983,.cpp

And CSV file is created at the specified location.

Conclusion

So, now you know how employ method 'csv' and likewise read and write data in CSV format. CSV files are widely used in software applications considering they are easy to read and manage, and their minor size makes them relatively fast for processing and transmission.

The csv module provides diverse functions and classes which allow you to read and write easily. You tin can look at the official Python documentation and find some more interesting tips and modules. CSV is the best fashion for saving, viewing, and sending data. Actually, it isn't and then hard to learn equally it seems at the beginning. Simply with a fiddling practice, you'll principal it.

Pandas is a great alternative to read CSV files.

Also, at that place are other means to parse text files with libraries like ANTLR, PLY, and PlyPlus. They can all handle heavy-duty parsing, and if unproblematic String manipulation doesn't piece of work, at that place are regular expressions which you tin can use.

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Source: https://www.guru99.com/python-csv.html

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