Neste tutorial, aprenderemos a escrever arquivos CSV com diferentes formatos em Python com a ajuda de exemplos.
Usaremos exclusivamente o csvmódulo integrado ao Python para essa tarefa. Mas primeiro, teremos que importar o módulo como:
import csv
Já cobrimos os princípios básicos de como usar o csvmódulo para ler e gravar em arquivos CSV. Se você não tem ideia de como usar o csvmódulo, confira nosso tutorial sobre Python CSV: Ler e escrever arquivos CSV
Uso básico de csv.writer ()
Vejamos um exemplo básico de csv.writer()como atualizar seu conhecimento existente.
Exemplo 1: Grave em arquivos CSV com csv.writer ()
Suponha que queremos escrever um arquivo CSV com as seguintes entradas:
SN, Nome, Contribuição 1, Linus Torvalds, Linux Kernel 2, Tim Berners-Lee, World Wide Web 3, Guido van Rossum, Python Programming
Veja como fazemos isso.
import csv with open('innovators.csv', 'w', newline='') as file: writer = csv.writer(file) writer.writerow(("SN", "Name", "Contribution")) writer.writerow((1, "Linus Torvalds", "Linux Kernel")) writer.writerow((2, "Tim Berners-Lee", "World Wide Web")) writer.writerow((3, "Guido van Rossum", "Python Programming"))
Quando executamos o programa acima, um arquivo innovators.csv é criado no diretório de trabalho atual com as entradas fornecidas.
Aqui, abrimos o arquivo innovators.csv no modo de escrita usando a open()função.
Para saber mais sobre como abrir arquivos em Python, visite: Entrada / Saída de Arquivos Python
Em seguida, a csv.writer()função é usada para criar um writerobjeto. A writer.writerow()função é então usada para gravar linhas únicas no arquivo CSV.
Exemplo 2: gravando várias linhas com gravadores ()
Se precisarmos gravar o conteúdo da lista bidimensional em um arquivo CSV, veja como podemos fazer isso.
import csv row_list = (("SN", "Name", "Contribution"), (1, "Linus Torvalds", "Linux Kernel"), (2, "Tim Berners-Lee", "World Wide Web"), (3, "Guido van Rossum", "Python Programming")) with open('protagonist.csv', 'w', newline='') as file: writer = csv.writer(file) writer.writerows(row_list)
A saída do programa é a mesma do Exemplo 1 .
Aqui, nossa lista bidimensional é passada para a writer.writerows()função de gravar o conteúdo da lista no arquivo CSV.
Agora vamos ver como podemos escrever arquivos CSV em diferentes formatos. Aprenderemos então como personalizar a csv.writer()função para escrevê-los.
Arquivos CSV com delimitadores personalizados
Por padrão, uma vírgula é usada como delimitador em um arquivo CSV. No entanto, alguns arquivos CSV podem usar delimitadores diferentes de vírgulas. Poucos são os populares |e .
Suponha que queiramos usar |como delimitador no arquivo innovators.csv do Exemplo 1 . Para escrever este arquivo, podemos passar um delimiterparâmetro adicional para a csv.writer()função.
Vamos dar um exemplo.
Exemplo 3: Gravar arquivo CSV com delimitador de tubulação
import csv data_list = (("SN", "Name", "Contribution"), (1, "Linus Torvalds", "Linux Kernel"), (2, "Tim Berners-Lee", "World Wide Web"), (3, "Guido van Rossum", "Python Programming")) with open('innovators.csv', 'w', newline='') as file: writer = csv.writer(file, delimiter='|') writer.writerows(data_list)
Resultado
SN | Nome | Contribuição 1 | Linus Torvalds | Linux Kernel 2 | Tim Berners-Lee | World Wide Web 3 | Guido van Rossum | Programação Python
Como podemos ver, o parâmetro opcional delimiter = '|'ajuda a especificar o writerobjeto que o arquivo CSV deve ter |como delimitador.
Arquivos CSV com citações
Alguns arquivos CSV têm aspas em torno de cada uma ou algumas das entradas.
Vamos pegar quotes.csv como exemplo, com as seguintes entradas:
"SN"; "Nome"; "Citações" 1; "Buda"; "O que pensamos que nos tornamos" 2; "Mark Twain"; "Nunca se arrependa de nada que o tenha feito sorrir" 3; "Oscar Wilde"; "Seja você mesmo Todos os outros já foram levados"
Usar csv.writer()por padrão não adicionará essas aspas às entradas.
Para adicioná-los, teremos que usar outro parâmetro opcional chamado quoting.
Vamos dar um exemplo de como aspas podem ser usadas em torno de valores não numéricos e ;como delimitadores.
Exemplo 4: escrever arquivos CSV com aspas
import csv row_list = ( ("SN", "Name", "Quotes"), (1, "Buddha", "What we think we become"), (2, "Mark Twain", "Never regret anything that made you smile"), (3, "Oscar Wilde", "Be yourself everyone else is already taken") ) with open('quotes.csv', 'w', newline='') as file: writer = csv.writer(file, quoting=csv.QUOTE_NONNUMERIC, delimiter=';') writer.writerows(row_list)
Resultado
"SN"; "Nome"; "Citações" 1; "Buda"; "O que pensamos que nos tornamos" 2; "Mark Twain"; "Nunca se arrependa de nada que o tenha feito sorrir" 3; "Oscar Wilde"; "Seja você mesmo Todos os outros já foram levados"
Aqui, o arquivo quotes.csv é criado no diretório de trabalho com as entradas acima.
Como você pode ver, passamos csv.QUOTE_NONNUMERICpara o quotingparâmetro. É uma constante definida pelo csvmódulo.
csv.QUOTE_NONNUMERICespecifica o writerobjeto que as aspas devem ser adicionadas às entradas não numéricas.
Existem 3 outras constantes predefinidas que você pode passar para o quotingparâmetro:
csv.QUOTE_ALL- Especifica owriterobjeto para gravar o arquivo CSV com aspas em torno de todas as entradas.csv.QUOTE_MINIMAL- Especifica owriterobjeto para citar apenas os campos que contêm caracteres especiais ( delimitador , quotechar ou quaisquer caracteres no determinador de linha )csv.QUOTE_NONE- Especifica owriterobjeto que nenhuma das entradas deve ser citada. É o valor padrão.
Arquivos CSV com citação personalizada
We can also write CSV files with custom quoting characters. For that, we will have to use an optional parameter called quotechar.
Let's take an example of writing quotes.csv file in Example 4, but with * as the quoting character.
Example 5: Writing CSV files with custom quoting character
import csv row_list = ( ("SN", "Name", "Quotes"), (1, "Buddha", "What we think we become"), (2, "Mark Twain", "Never regret anything that made you smile"), (3, "Oscar Wilde", "Be yourself everyone else is already taken") ) with open('quotes.csv', 'w', newline='') as file: writer = csv.writer(file, quoting=csv.QUOTE_NONNUMERIC, delimiter=';', quotechar='*') writer.writerows(row_list)
Output
*SN*;*Name*;*Quotes* 1;*Buddha*;*What we think we become* 2;*Mark Twain*;*Never regret anything that made you smile* 3;*Oscar Wilde*;*Be yourself everyone else is already taken*
Here, we can see that quotechar='*' parameter instructs the writer object to use * as quote for all non-numeric values.
Dialects in CSV module
Notice in Example 5 that we have passed multiple parameters (quoting, delimiter and quotechar) to the csv.writer() function.
This practice is acceptable when dealing with one or two files. But it will make the code more redundant and ugly once we start working with multiple CSV files with similar formats.
As a solution to this, the csv module offers dialect as an optional parameter.
Dialect helps in grouping together many specific formatting patterns like delimiter, skipinitialspace, quoting, escapechar into a single dialect name.
It can then be passed as a parameter to multiple writer or reader instances.
Example 6: Write CSV file using dialect
Suppose we want to write a CSV file (office.csv) with the following content:
"ID"|"Name"|"Email" "A878"|"Alfonso K. Hamby"|"[email protected]" "F854"|"Susanne Briard"|"[email protected]" "E833"|"Katja Mauer"|"[email protected]"
The CSV file has quotes around each entry and uses | as a delimiter.
Instead of passing two individual formatting patterns, let's look at how to use dialects to write this file.
import csv row_list = ( ("ID", "Name", "Email"), ("A878", "Alfonso K. Hamby", "[email protected]"), ("F854", "Susanne Briard", "[email protected]"), ("E833", "Katja Mauer", "[email protected]") ) csv.register_dialect('myDialect', delimiter='|', quoting=csv.QUOTE_ALL) with open('office.csv', 'w', newline='') as file: writer = csv.writer(file, dialect='myDialect') writer.writerows(row_list)
Output
"ID"|"Name"|"Email" "A878"|"Alfonso K. Hamby"|"[email protected]" "F854"|"Susanne Briard"|"[email protected]" "E833"|"Katja Mauer"|"[email protected]"
Here, office.csv is created in the working directory with the above contents.
From this example, we can see that the csv.register_dialect() function is used to define a custom dialect. Its syntax is:
csv.register_dialect(name(, dialect(, **fmtparams)))
The custom dialect requires a name in the form of a string. Other specifications can be done either by passing a sub-class of the Dialect class, or by individual formatting patterns as shown in the example.
While creating the writer object, we pass dialect='myDialect' to specify that the writer instance must use that particular dialect.
The advantage of using dialect is that it makes the program more modular. Notice that we can reuse myDialect to write other CSV files without having to re-specify the CSV format.
Write CSV files with csv.DictWriter()
The objects of csv.DictWriter() class can be used to write to a CSV file from a Python dictionary.
The minimal syntax of the csv.DictWriter() class is:
csv.DictWriter(file, fieldnames)
Here,
file- CSV file where we want to write tofieldnames- alistobject which should contain the column headers specifying the order in which data should be written in the CSV file
Example 7: Python csv.DictWriter()
import csv with open('players.csv', 'w', newline='') as file: fieldnames = ('player_name', 'fide_rating') writer = csv.DictWriter(file, fieldnames=fieldnames) writer.writeheader() writer.writerow(('player_name': 'Magnus Carlsen', 'fide_rating': 2870)) writer.writerow(('player_name': 'Fabiano Caruana', 'fide_rating': 2822)) writer.writerow(('player_name': 'Ding Liren', 'fide_rating': 2801))
Output
The program creates a players.csv file with the following entries:
player_name,fide_rating Magnus Carlsen,2870 Fabiano Caruana,2822 Ding Liren,2801
The full syntax of the csv.DictWriter() class is:
csv.DictWriter(f, fieldnames, restval='', extrasaction='raise', dialect='excel', *args, **kwds)
To learn more about it in detail, visit: Python csv.DictWriter() class
CSV files with lineterminator
A lineterminator is a string used to terminate lines produced by writer objects. The default value is . You can change its value by passing any string as a lineterminator parameter.
However, the reader object only recognizes or as lineterminator values. So using other characters as line terminators is highly discouraged.
doublequote & escapechar in CSV module
In order to separate delimiter characters in the entries, the csv module by default quotes the entries using quotation marks.
So, if you had an entry: He is a strong, healthy man, it will be written as: "He is a strong, healthy man".
Similarly, the csv module uses double quotes in order to escape the quote character present in the entries by default.
If you had an entry: Go to "programiz.com", it would be written as: "Go to ""programiz.com""".
Here, we can see that each " is followed by a " to escape the previous one.
doublequote
It handles how quotechar present in the entry themselves are quoted. When True, the quoting character is doubled and when False, the escapechar is used as a prefix to the quotechar. By default its value is True.
escapechar
escapechar parameter is a string to escape the delimiter if quoting is set to csv.QUOTE_NONE and quotechar if doublequote is False. Its default value is None.
Example 8: Using escapechar in csv writer
import csv row_list = ( ('Book', 'Quote'), ('Lord of the Rings', '"All we have to decide is what to do with the time that is given us."'), ('Harry Potter', '"It matters not what someone is born, but what they grow to be."') ) with open('book.csv', 'w', newline='') as file: writer = csv.writer(file, escapechar='/', quoting=csv.QUOTE_NONE) writer.writerows(row_list)
Output
Book,Quote Lord of the Rings,/"All we have to decide is what to do with the time that is given us./" Harry Potter,/"It matters not what someone is born/, but what they grow to be./"
Here, we can see that / is prefix to all the " and , because we specified quoting=csv.QUOTE_NONE.
If it wasn't defined, then, the output would be:
Book,Quote Lord of the Rings,"""All we have to decide is what to do with the time that is given us.""" Harry Potter,"""It matters not what someone is born, but what they grow to be."""
Since we allow quoting, the entries with special characters(" in this case) are double-quoted. The entries with delimiter are also enclosed within quote characters.(Starting and closing quote characters)
The remaining quote characters are to escape the actual " present as part of the string, so that they are not interpreted as quotechar.
Note: The csv module can also be used for other file extensions (like: .txt) as long as their contents are in proper structure.
Leitura recomendada: leia arquivos CSV em Python
