Python Csv To Dictionary
(Sponsors) Get started learning Python with free. Learn Data Science by completing interactive coding challenges and watching videos by expert instructors.What is CSV File?CSV (Comma-separated values) is a common data exchange format used by the applications to produce and consume data. Some other well-known data exchange formats are XML, HTML, JSON etc.A CSV file is a simple text file where each line contains a list of values (or fields) delimited by commas.Although the term “Comma” appears in the format name itself, but you will encounter CSV files where data is delimited using tab ( t) or pipe ( ) or any other character that can be used as a delimiter.The first line of the CSV file represents the header containing a list of column names in the file. The header is optional but highly recommended.The CSV file is commonly used to represent tabular data. For example, consider the following table: IDNameCountryCodeDistrictPopulation1KabulAFGKabol17800002QandaharAFGQandahar2375003HeratAFGHerat1868004Mazar-e-SharifAFGBalkh1278005AmsterdamNLDNoord-Holland731200The above table can be represented using CSV format as follows. 2,Tom,'The Magician'It is important to note that the CSV format is not fully standardized.
So the rules we have just mentioned are not universal. Once in a while, you will encounter CSV files that have a different way of representing fields.Fortunately, to make things easier for us Python provides the csv module.Before we start reading and writing CSV files, you should have a good understanding of how to work with files in general. If you need a refresher, consider reading.The csv module is used for reading and writing files. It mainly provides following classes and functions:. reader ( ).
writer ( ). DictReader ( ). DictWriter ( )Let’s start with the reader ( ) function. Reading a CSV File with readerThe reader ( ) function takes a file object and returns a csv. Reader object that can be used to iterate over the contents of a CSV file. The syntax of reader ( ) function is as follows:Syntax: reader ( fileobj , dialect = 'excel' ,. fmtparam ) - csv.
Reader ArgumentDescriptionfileobj(required) It refers to the file objectdialect(optional) Dialect refers to the different ways of formatting the CSV document. By default, the csv module uses the same format as Microsoft Excel.
We will discuss dialect in detail later in this post.fmtparam(optional) It refers to the set of keyword arguments to customize the dialect (see the next section).Let’s say we have following CSV file:employees.csv. 3 Mary mary@mail.comCustomizing the readerBy default, the csv module works according to the format used by Microsoft excel, but you can also define your own format using something called Dialect.The following are some additional arguments that you can pass to the reader ( ) function to customize its working. delimiter – It refers to the character used to separate values (or fields) in the CSV file. It defaults to comma (, ). skipinitialspace – It controls how the space following the delimiter will be interpreted. If True, the initial whitespaces will be removed. It defaults to False.
lineterminator – It refers to the character sequence used to terminate the line. It defaults to r n.
quotechar – It refers to the single character string that will be used to quote values if special characters (like delimiter) appears inside the field. It defaults to '. quoting – controls when quotes should be generated by the writer or recognized by the reader. It can take one of the following constants:.
csv. QUOTEMINIMAL means add quote only when required, for example, when afield contains either the quotechar or the delimiter. This is the default. csv. QUOTEALL means quotes everything regardless of the field type.
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csv. QUOTENONNUMERIC means quotes everything except integers and floats. csv. QUOTENONE means that do not quote anything on output.
However, while reading quotes are included around the field values. escapechar – It refers to the one-character string used to escapethe delimiter when quoting is set to QUOTENONE. It defaults to None. doublequote – controls the handling of quotes inside fields. WhenTrue, two consecutive quotes are interpreted as one during read,and when writing, each quote character embedded in the data iswritten as two quotes.Let’s workthrough some examples to better understand how these arguments work: delimiter argumentemployeespipe.csv.
'Name', 'Team', 'Position', 'Height(inches)', 'Weight(lbs)', 'Age'Adam Donachie', 'BAL', 'Catcher', '74', '180', '22.99'Paul Bako', 'BAL', 'Catcher', '74', '215', '34.69'Ramon Hernandez', 'BAL', 'Catcher', '72', '210', '30.78'Kevin Millar', 'BAL', 'First Baseman', '72', '210', '35.43'Chris Gomez', 'BAL', 'First Baseman', '73', '188', '35.71'Brian Roberts', 'BAL', 'Second Baseman', '69', '176', '29.39'Miguel Tejada', 'BAL', 'Shortstop', '69', '209', '30.77'Melvin Mora', 'BAL', 'Third Baseman', '71', '200', '35.07'. '4', 'Keziah Chaney', 'The librarian whispered to us, 'The sign on the wall says 'Quiet'Writing CSV files with writerTo write data to a CSV file we use the writer ( ) function. It accepts the same argument as the reader ( ) function but returns a writer object (i.e csv. Writer):Syntax: writer ( fileobj , dialect = 'excel' ,. fmtparam ) - & amp; gt; csvwriter ArgumentDescriptionfileobj(required) It refers to the file objectdialect(optional) Dialect refers to the different ways of formatting the CSV document. By default, the csv module uses the same format as Microsoft Excel.
We will discuss dialect in detail later in this post.fmtparam(optional) Formatting parameters, work same as the reader ( )’s function.The writer instance provides the following two methods to write data: MethodDescriptionwriterow ( row )Writes a single row of data and returns the number of characters written. The row must be a sequence of strings and number.writerows ( rows )Writes multiple rows of data and returns None. The rows must be a sequence.Here are examples:Example 1: Using writerow ( ). Import csvheader = 'id', 'name', 'address', 'zip'rows = 1, 'Hannah', '4891 Blackwell Street, Anchorage, Alaska', 99503 ,2, 'Walton', '4223 Half and Half Drive, Lemoore, California', 97401 ,3, 'Sam', '3952 Little Street, Akron, Ohio', 93704,4, 'Chris', '3192 Flinderation Road, Arlington Heights, Illinois', 62677,5, 'Doug', '3236 Walkers Ridge Way, Burr Ridge', 61257,with open('customers.csv', 'wt') as f:csvwriter = csv.writer(f)csvwriter.writerow(header) # write headerfor row in rows:csvwriter.writerow(row). Import csvheader = 'id', 'name', 'address', 'zip'rows = 1, 'Hannah', '4891 Blackwell Street, Anchorage, Alaska', 99503 ,2, 'Walton', '4223 Half and Half Drive, Lemoore, California', 97401 ,3, 'Sam', '3952 Little Street, Akron, Ohio', 93704,4, 'Chris', '3192 Flinderation Road, Arlington Heights, Illinois', 62677,5, 'Doug', '3236 Walkers Ridge Way, Burr Ridge', 61257,with open('customers.csv', 'wt') as f:csvwriter = csv.writer(f)csvwriter.writerow(header) # write headercsvwriter.writerows(rows). Import csvheader = 'id', 'name', 'address', 'zip'rows = 1, 'Hannah', '4891 Blackwell Street, Anchorage, Alaska', 99503 ,2, 'Walton', '4223 Half and Half Drive, Lemoore, California', 97401 ,3, 'Sam', '3952 Little Street, Akron, Ohio', 93704,4, 'Chris', '3192 Flinderation Road, Arlington Heights, Illinois', 62677,5, 'Doug', '3236 Walkers Ridge Way, Burr Ridge', 61257,with open('customers.csv', 'wt') as f:csvwriter = csv.writer(f, quoting=csv.QUOTENONNUMERIC)csvwriter.writerow(header) # write headercsvwriter.writerows(rows).
Import csvheader = 'id', 'name', 'address', 'zip'rows = 1, 'Hannah', '4891 Blackwell Street, Anchorage, Alaska', 99503 ,2, 'Walton', '4223 Half and Half Drive, Lemoore, California', 97401 ,3, 'Sam', '3952 Little Street, Akron, Ohio', 93704,4, 'Chris', '3192 Flinderation Road, Arlington Heights, Illinois', 62677,5, 'Doug', '3236 Walkers Ridge Way, Burr Ridge', 61257,with open('customers.csv', 'wt') as f:csvwriter = csv.writer(f, quoting=csv.QUOTEALL)csvwriter.writerow(header) # write headercsvwriter.writerows(rows). Import csvheader = 'id', 'name', 'address', 'zip'rows = 1, 'Hannah', '4891 Blackwell Street, Anchorage, Alaska', 99503 ,2, 'Walton', '4223 Half and Half Drive, Lemoore, California', 97401 ,3, 'Sam', '3952 Little Street, Akron, Ohio', 93704,4, 'Chris', '3192 Flinderation Road, Arlington Heights, Illinois', 62677,5, 'Doug', '3236 Walkers Ridge Way, Burr Ridge', 61257,with open('customers.csv', 'wt') as f:csvwriter = csv.writer(f, quotechar=')csvwriter.writerow(header) # write headercsvwriter.writerows(rows). Import csvheader = 'id', 'name', 'address', 'zip'rows = 1, 'Hannah', '4891 Blackwell Street, Anchorage, Alaska', 99503 ,2, 'Walton', '4223 Half and Half Drive, Lemoore, California', 97401 ,3, 'Sam', '3952 Little Street, Akron, Ohio', 93704,4, 'Chris', '3192 Flinderation Road, Arlington Heights, Illinois', 62677,5, 'Doug', '3236 Walkers Ridge Way, Burr Ridge', 61257,with open('customers.csv', 'wt') as f:csvwriter = csv.writer(f, quoting=csv.QUOTENONE)csvwriter.writerow(header) # write headercsvwriter.writerows(rows). Import csvheader = 'id', 'name', 'address', 'zip'rows = 1, 'Hannah', '4891 Blackwell Street, Anchorage, Alaska', 99503 ,2, 'Walton', '4223 Half and Half Drive, Lemoore, California', 97401 ,3, 'Sam', '3952 Little Street, Akron, Ohio', 93704,4, 'Chris', '3192 Flinderation Road, Arlington Heights, Illinois', 62677,5, 'Doug', '3236 Walkers Ridge Way, Burr Ridge', 61257,with open('customers.csv', 'wt') as f:csvwriter = csv.writer(f, quoting=csv.QUOTENONE, escapechar=')csvwriter.writerow(header) # write headercsvwriter.writerows(rows). 5,Doug,3236 Walkers Ridge Way, Burr Ridge,61257Notice that the commas (,) in the address field is escaped using the backslash ( ) character.You should now have a good understanding of various formatting arguments and the context in which they are used with the reader ( ) and writer ( ) function. In the next section will see some other ways to read and write data. Reading a CSV file with DictReaderDictReader works almost exactly like reader ( ) but instead of retuning a line as a list, it returns a dictionary.
Python Csv To Dictionary File
Its syntax is as follows:Syntax:: DictReader ( fileobj, fieldnames = None, restkey = None, restval = None, dialect = 'excel',. fmtparam ) ArgumentDescriptionfileobj(required) It refers to the file object.fieldnames(optional) It refers to the list of keys that will be used in the returned dictionary in order. If omitted, the field names are inferred from the first row of the CSV file.restkey(optional) If the row has more fields than specified in the fieldnames parameter, then the remaining fields is stored as a sequence keyed by the value of restkey argument.restval(optional) It provides value to fields which are missing from the input.dialect(optional) Dialect refers to the different ways of formatting the CSV document. By default, the csv module uses the same format as Microsoft excel. We will discuss dialect in detail later in this post.fmtparamIt refers to formatting arguments and works exactly like reader ( ) and writer ( ).Let’s take some examples:Example 1:customers.csv. 5,Doug,'3236 Walkers Ridge Way, Burr Ridge'Creating DialectEarlier in this post, we have learned various formatting parameters that allow us to customize the reader and writer object to accommodate for differences in the CSV conventions.If you find yourself passing the same set of formatting parameters over and over again.
Consider creating your own Dialect.A dialect object or (simply dialect) is a way to group various formatting parameters. Once you have created the dialect object, simply pass it to the reader or writer, rather than passing each formatting argument separately.To create a new dialect, we use registerdialect ( ) function. It accepts dialect name as a string and one or more formatting parameters as keyword arguments.The following table lists all the formatting arguments along with their default values: ArgumentDefaultDescriptiondelimiter,It refers to the character used to separate values (or fields) in the CSV file.skipinitialspaceFalseIt controls how the space following the delimiter will be interpreted. If True, the initial whitespaces will be removed.lineterminator r nIt refers to the character sequence used to terminate the line.quotechar'It refers to the single character string that will be used to quote values if special characters (like delimiter) appears inside the field.quotingcsv.
QUOTENONEcontrols when quotes should be generated by the writer or recognized by the reader (see above for other options).escapecharNoneIt refers to the one-character string used to escape the delimiter when quoting is set to.doublequoteTruecontrols the handling of quotes inside fields. When True, two consecutive quotes are interpreted as one during read, and when writing, each quote character embedded in the data is written as two quotes.Let’s create a simple dialect.