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This module implements a simple high performance CSV (comma separated value) parser.

Basic usage

import std/parsecsv
from std/os import paramStr
from std/streams import newFileStream

var s = newFileStream(paramStr(1), fmRead)
if s == nil:
  quit("cannot open the file" & paramStr(1))

var x: CsvParser
open(x, s, paramStr(1))
while readRow(x):
  echo "new row: "
  for val in items(x.row):
    echo "##", val, "##"
close(x)

For CSV files with a header row, the header can be read and then used as a reference for item access with rowEntry:

import std/parsecsv

# Prepare a file
let content = """One,Two,Three,Four
1,2,3,4
10,20,30,40
100,200,300,400
"""
writeFile("temp.csv", content)

var p: CsvParser
p.open("temp.csv")
p.readHeaderRow()
while p.readRow():
  echo "new row: "
  for col in items(p.headers):
    echo "##", col, ":", p.rowEntry(col), "##"
p.close()

Imports

lexbase, streams, os

Types

CsvError = object of IOError

An exception that is raised if a parsing error occurs. Source Edit

CsvParser = object of BaseLexer
  row*: CsvRow
  headers*: seq[string]

The parser object.

It consists of two public fields:

row is the current row
headers are the columns that are defined in the csv file (read using readHeaderRow). Used with rowEntry).

Source Edit

CsvRow = seq[string]

A row in a CSV file. Source Edit

Procs

proc close(self: var CsvParser) {.inline, ...raises: [IOError, OSError], tags: [WriteIOEffect], forbids: [].}: Closes the parser self and its associated input stream. Source Edit
proc open(self: var CsvParser; filename: string; separator = ','; quote = '\"'; escape = '\x00'; skipInitialSpace = false) {. ...raises: [CsvError, IOError, OSError], tags: [ReadIOEffect], forbids: [].}: Similar to the other open proc, but creates the file stream for you.
Example:

from std/os import removeFile writeFile("tmp.csv", "One,Two,Three\n1,2,3\n10,20,300") var parser: CsvParser parser.open("tmp.csv") parser.close() removeFile("tmp.csv")
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proc open(self: var CsvParser; input: Stream; filename: string; separator = ','; quote = '\"'; escape = '\x00'; skipInitialSpace = false) {. ...raises: [IOError, OSError], tags: [ReadIOEffect], forbids: [].}: Initializes the parser with an input stream. Filename is only used for nice error messages. The parser's behaviour can be controlled by the diverse optional parameters:
separator: character used to separate fields

quote: Used to quote fields containing special characters like separator, quote or new-line characters. '\0' disables the parsing of quotes.

escape: removes any special meaning from the following character; '\0' disables escaping; if escaping is disabled and quote is not '\0', two quote characters are parsed one literal quote character.

skipInitialSpace: If true, whitespace immediately following the separator is ignored.

See also:

open proc which creates the file stream for you

Example:

import std/streams var strm = newStringStream("One,Two,Three\n1,2,3\n10,20,30") var parser: CsvParser parser.open(strm, "tmp.csv") parser.close() strm.close()
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proc processedRows(self: var CsvParser): int {.inline, ...raises: [], tags: [], forbids: [].}: Returns number of the processed rows.

But even if readRow arrived at EOF then processed rows counter is incremented.

Example:

import std/streams var strm = newStringStream("One,Two,Three\n1,2,3") var parser: CsvParser parser.open(strm, "tmp.csv") doAssert parser.readRow() doAssert parser.processedRows() == 1 doAssert parser.readRow() doAssert parser.processedRows() == 2 ## Even if `readRow` arrived at EOF then `processedRows` is incremented. doAssert parser.readRow() == false doAssert parser.processedRows() == 3 doAssert parser.readRow() == false doAssert parser.processedRows() == 4 parser.close() strm.close()
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proc readHeaderRow(self: var CsvParser) {....raises: [IOError, OSError, CsvError], tags: [ReadIOEffect], forbids: [].}: Reads the first row and creates a look-up table for column numbers See also:
rowEntry proc

Example:

import std/streams var strm = newStringStream("One,Two,Three\n1,2,3") var parser: CsvParser parser.open(strm, "tmp.csv") parser.readHeaderRow() doAssert parser.headers == @["One", "Two", "Three"] doAssert parser.row == @["One", "Two", "Three"] doAssert parser.readRow() doAssert parser.headers == @["One", "Two", "Three"] doAssert parser.row == @["1", "2", "3"] parser.close() strm.close()
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proc readRow(self: var CsvParser; columns = 0): bool {. ...raises: [IOError, OSError, CsvError], tags: [ReadIOEffect], forbids: [].}: Reads the next row; if columns > 0, it expects the row to have exactly this many columns. Returns false if the end of the file has been encountered else true.

Blank lines are skipped.

Example:

import std/streams var strm = newStringStream("One,Two,Three\n1,2,3\n\n10,20,30") var parser: CsvParser parser.open(strm, "tmp.csv") doAssert parser.readRow() doAssert parser.row == @["One", "Two", "Three"] doAssert parser.readRow() doAssert parser.row == @["1", "2", "3"] ## Blank lines are skipped. doAssert parser.readRow() doAssert parser.row == @["10", "20", "30"] var emptySeq: seq[string] doAssert parser.readRow() == false doAssert parser.row == emptySeq doAssert parser.readRow() == false doAssert parser.row == emptySeq parser.close() strm.close()
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proc rowEntry(self: var CsvParser; entry: string): var string {. ...raises: [KeyError], tags: [], forbids: [].}: Accesses a specified entry from the current row.

Assumes that readHeaderRow has already been called.

If specified entry does not exist, raises KeyError.

Example:

import std/streams var strm = newStringStream("One,Two,Three\n1,2,3\n\n10,20,30") var parser: CsvParser parser.open(strm, "tmp.csv") ## Requires calling `readHeaderRow`. parser.readHeaderRow() doAssert parser.readRow() doAssert parser.rowEntry("One") == "1" doAssert parser.rowEntry("Two") == "2" doAssert parser.rowEntry("Three") == "3" doAssertRaises(KeyError): discard parser.rowEntry("NonexistentEntry") parser.close() strm.close()
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std/parsecsv

Basic usage

See also

Imports

Types

Procs