8.8. CSV DictWriter¶
Writes iterable of dicts (eg. list[dict]) to CSV file
csv.DictWriter()Remember to add
mode='w'toopen()functionDefault encoding is
encoding='utf-8'
8.8.1. SetUp¶
>>> import csv
>>> from pathlib import Path
8.8.2. Minimal¶
>>> DATA = [
... {'sepal_length': 5.4, 'sepal_width': 3.9, 'petal_length': 1.3, 'petal_width': 0.4, 'species': 'setosa'},
... {'sepal_length': 5.9, 'sepal_width': 3.0, 'petal_length': 5.1, 'petal_width': 1.8, 'species': 'virginica'},
... {'sepal_length': 6.0, 'sepal_width': 3.4, 'petal_length': 4.5, 'petal_width': 1.6, 'species': 'versicolor'},
... ]
>>>
>>> header = DATA[0].keys()
>>>
>>> with open('/tmp/myfile.csv', mode='w') as file:
... result = csv.DictWriter(file, fieldnames=header)
... result.writeheader()
... result.writerows(DATA)
59
Result:
>>> print(Path('/tmp/myfile.csv').read_text())
sepal_length,sepal_width,petal_length,petal_width,species
5.4,3.9,1.3,0.4,setosa
5.9,3.0,5.1,1.8,virginica
6.0,3.4,4.5,1.6,versicolor
8.8.3. Parametrized¶
>>> DATA = [
... {'sepal_length': 5.4, 'sepal_width': 3.9, 'petal_length': 1.3, 'petal_width': 0.4, 'species': 'setosa'},
... {'sepal_length': 5.9, 'sepal_width': 3.0, 'petal_length': 5.1, 'petal_width': 1.8, 'species': 'virginica'},
... {'sepal_length': 6.0, 'sepal_width': 3.4, 'petal_length': 4.5, 'petal_width': 1.6, 'species': 'versicolor'},
... ]
>>>
>>>
>>> header = DATA[0].keys()
>>>
>>> with open('/tmp/myfile.csv', mode='w', encoding='utf-8') as file:
... result = csv.DictWriter(file, fieldnames=header, quotechar='"', delimiter=';', quoting=csv.QUOTE_ALL)
... result.writeheader()
... result.writerows(DATA)
69
Result:
>>> print(Path('/tmp/myfile.csv').read_text())
"sepal_length";"sepal_width";"petal_length";"petal_width";"species"
"5.4";"3.9";"1.3";"0.4";"setosa"
"5.9";"3.0";"5.1";"1.8";"virginica"
"6.0";"3.4";"4.5";"1.6";"versicolor"
8.8.4. Assignments¶
"""
* Assignment: CSV DictWriter Fixed
* Complexity: easy
* Lines of code: 4 lines
* Time: 5 min
English:
1. Using `csv.DictWriter()` save `DATA` to `FILE`
2. Open file in your spreadsheet program like:
Microsoft Excel, Libre Office or Numbers etc.
3. Open file in simple in your IDE and simple text editor like:
Notepad, vim, gedit
4. Non functional requirements:
a. All fields must be enclosed by double quote `"` character
b. Use `,` to separate columns
d. Use Unix `\n` line terminator
5. Run doctests - all must succeed
Polish:
1. Za pomocą `csv.DictWriter()` zapisz `DATA` do `FILE`
2. Spróbuj otworzyć plik w arkuszu kalkulacyjnym tj.
Microsoft Excel, Libre Office lub Numbers itp
3. Spróbuj otworzyć plik w IDE i prostym edytorze tekstu tj.
Notepad, vim lub gedit
4. Wymagania niefunkcjonalne:
a. Wszystkie pola muszą być otoczone znakiem cudzysłowu `"`
b. Użyj `,` do oddzielenia kolumn
d. Użyj zakończenia linii Unix `\n`
5. Uruchom doctesty - wszystkie muszą się powieść
Hint:
* For Python before 3.8: `dict(OrderedDict)`
Tests:
>>> import sys; sys.tracebacklimit = 0
>>> from os import remove
>>> result = open(FILE).read()
>>> remove(FILE)
>>> assert result is not Ellipsis, \
'Assign result to variable: `result`'
>>> assert type(result) is str, \
'Variable `result` has invalid type, should be str'
>>> print(result) # doctest: +NORMALIZE_WHITESPACE
"firstname","lastname","age"
"Mark","Watney","42"
"Melissa","Lewis","41"
"Rick","Martinez","40"
"Alex","Vogel","42"
"Beth","Johanssen","29"
"Chris","Beck","36"
<BLANKLINE>
"""
import csv
DATA = [
{'firstname': 'Mark', 'lastname': 'Watney', 'age': 42},
{'firstname': 'Melissa', 'lastname': 'Lewis', 'age': 41},
{'firstname': 'Rick', 'lastname': 'Martinez', 'age': 40},
{'firstname': 'Alex', 'lastname': 'Vogel', 'age': 42},
{'firstname': 'Beth', 'lastname': 'Johanssen', 'age': 29},
{'firstname': 'Chris', 'lastname': 'Beck', 'age': 36},
]
FILE = r'_temporary.csv'
# Write DATA to FILE, generate header from DATA
# type: ContextManager
with open(FILE, mode='w') as file:
...
"""
* Assignment: CSV DictWriter Schemaless
* Complexity: medium
* Lines of code: 7 lines
* Time: 5 min
English:
1. Using `csv.DictWriter()` write variable schema data to `FILE`
2. `fieldnames` must be automatically generated from `DATA`
3. Non functional requirements:
a. All fields must be enclosed by double quote `"` character
b. Use `,` to separate columns
c. Use `utf-8` encoding
d. Use Unix `\n` line terminator
e. Sort `fieldnames` using `sorted()`
4. Run doctests - all must succeed
Polish:
1. Za pomocą `csv.DictWriter()` zapisz dane o zmiennej strukturze do `FILE`
2. `fieldnames` musi być generowane automatycznie na podstawie `DATA`
3. Wymagania niefunkcjonalne:
a. Wszystkie pola muszą być otoczone znakiem cudzysłowu `"`
b. Użyj `,` do oddzielenia kolumn
c. Użyj kodowania `utf-8`
d. Użyj zakończenia linii Unix `\n`
e. Posortuj `fieldnames` używając `sorted()`
4. Uruchom doctesty - wszystkie muszą się powieść
Tests:
>>> import sys; sys.tracebacklimit = 0
>>> from os import remove
>>> result = open(FILE).read()
>>> remove(FILE)
>>> assert result is not Ellipsis, \
'Assign result to variable: `result`'
>>> assert type(result) is str, \
'Variable `result` has invalid type, should be str'
>>> print(result)
"petal_length","petal_width","sepal_length","sepal_width","species"
"","","5.1","3.5","setosa"
"4.1","1.3","","","versicolor"
"","1.8","6.3","","virginica"
"","0.2","5.0","","setosa"
"4.1","","","2.8","versicolor"
"","1.8","","2.9","virginica"
<BLANKLINE>
"""
import csv
DATA = [
{'sepal_length': 5.1, 'sepal_width': 3.5, 'species': 'setosa'},
{'petal_length': 4.1, 'petal_width': 1.3, 'species': 'versicolor'},
{'sepal_length': 6.3, 'petal_width': 1.8, 'species': 'virginica'},
{'sepal_length': 5.0, 'petal_width': 0.2, 'species': 'setosa'},
{'sepal_width': 2.8, 'petal_length': 4.1, 'species': 'versicolor'},
{'sepal_width': 2.9, 'petal_width': 1.8, 'species': 'virginica'},
]
FILE = r'_temporary.csv'
# Write DATA to FILE, generate header from DATA
# type: ContextManager
with open(FILE, mode='w', encoding='utf-8') as file:
...
"""
* Assignment: CSV DictWriter Objects
* Complexity: medium
* Lines of code: 6 lines
* Time: 8 min
English:
1. Using `csv.DictWriter()` save data to `FILE`
2. Non-functional requirements:
a. Use `,` to separate columns
b. Use `utf-8` encoding
c. Use Unix `\n` line terminator
d. sort header (fieldnames)
3. Run doctests - all must succeed
Polish:
1. Za pomocą `csv.DictWriter()` zapisz dane do `FILE`
2. Wymagania niefunkcjonalne:
a. Użyj `,` do oddzielenia kolumn
b. Użyj kodowania `utf-8`
c. Użyj zakończenia linii Unix `\n`
d. posortuj nagłówek (fieldnames)
3. Uruchom doctesty - wszystkie muszą się powieść
Hints:
* `vars()`
Tests:
>>> import sys; sys.tracebacklimit = 0
>>> from os import remove
>>> result = open(FILE).read()
>>> remove(FILE)
>>> assert result is not Ellipsis, \
'Assign result to variable: `result`'
>>> assert type(result) is str, \
'Variable `result` has invalid type, should be str'
>>> print(result)
petal_length,petal_width,sepal_length,sepal_width,species
1.4,0.2,5.1,3.5,setosa
5.1,1.9,5.8,2.7,virginica
1.4,0.2,5.1,3.5,setosa
4.1,1.3,5.7,2.8,versicolor
5.6,1.8,6.3,2.9,virginica
4.5,1.5,6.4,3.2,versicolor
<BLANKLINE>
"""
import csv
class Iris:
def __init__(self, sepal_length, sepal_width,
petal_length, petal_width, species):
self.sepal_length = sepal_length
self.sepal_width = sepal_width
self.petal_length = petal_length
self.petal_width = petal_width
self.species = species
DATA = [
Iris(5.1, 3.5, 1.4, 0.2, 'setosa'),
Iris(5.8, 2.7, 5.1, 1.9, 'virginica'),
Iris(5.1, 3.5, 1.4, 0.2, 'setosa'),
Iris(5.7, 2.8, 4.1, 1.3, 'versicolor'),
Iris(6.3, 2.9, 5.6, 1.8, 'virginica'),
Iris(6.4, 3.2, 4.5, 1.5, 'versicolor'),
]
FILE = r'_temporary.txt'
# Write DATA to FILE, generate header from DATA
# type: ContextManager
with open(FILE, mode='w', encoding='utf-8') as file:
...