TopolearnInteroperating with databases and strict parsers often requires a specific quoting style.
The quoting parameter controls when the writer quotes fields, and how the reader interprets quotes:
QUOTE_MINIMAL(default): only fields containing special characters.QUOTE_ALL: every field.QUOTE_NONNUMERIC: all non-numeric fields; the reader converts unquoted fields to float.QUOTE_NONE: never quote. The writer then needs anescapecharto escape delimiters, or it raisescsv.Error.QUOTE_STRINGS(3.12+): quote all strings;Noneis written as an empty, unquoted field. The reader turns unquoted empty fields intoNoneand other unquoted fields into floats.QUOTE_NOTNULL(3.12+): quote everything exceptNone, which is written empty; the reader turns unquoted empty fields intoNone.
The last two finally let a CSV round trip distinguish None (,,) from an empty string (,"",), which databases care about.
Quote characters inside fields: with doublequote=True (default) a " is written as "". With doublequote=False, the writer uses escapechar instead (\").
Newlines inside fields are legal when quoted: the reader returns one record spanning several physical lines. Tools that process CSV line by line (wc -l, grep, naive splitting) miscount such files.
Example
import csv, io
def write(rows, **kw):
buf = io.StringIO()
csv.writer(buf, lineterminator="\n", **kw).writerows(rows)
return buf.getvalue()
rows = [["id", "note", "score"], [1, "", None], [2, 'say "ok" now', 3.5]]
print(write(rows, quoting=csv.QUOTE_ALL), end="")
# "id","note","score" / "1","","" / "2","say ""ok"" now","3.5"
print(write(rows, quoting=csv.QUOTE_NOTNULL), end="")
# "id","note","score" / "1","", / "2","say ""ok"" now","3.5"
print(write([["a,b", 'q"']], quoting=csv.QUOTE_NONE, escapechar="\\"), end="")
# a\,b,q\"
back = csv.reader(io.StringIO('"x","",\n'), quoting=csv.QUOTE_NOTNULL)
print(next(back)) # ['x', '', None]Remember
- QUOTE_MINIMAL, ALL, NONNUMERIC, NONE, STRINGS, NOTNULL control quoting
- QUOTE_NOTNULL / QUOTE_STRINGS (3.12) distinguish None from empty strings
- QUOTE_NONE needs an escapechar for special characters
Watch out for
- Counting CSV records with wc -l when quoted fields contain newlines.