Question

我正在尝试从Netezza导出一个大文件（使用Netezza ODBC + pyodbc），这个解决方案会抛出memoryError，如果我循环没有“list”，那就非常慢。你有没有想到一个不会杀死我的服务器/ python进程但可以更快运行的中间解决方案？

cursorNZ.execute(sql)
archi = open("c:\test.csv", "w")
lista = list(cursorNZ.fetchall())
for fila  in lista:
    registro = ''
    for campo in fila:
        campo = str(campo)
        registro = registro+str(campo)+";"
    registro = registro[:-1]
    registro = registro.replace('None','NULL')
    registro = registro.replace("'NULL'","NULL")
    archi.write(registro+"\n")

----编辑----

谢谢，我正在尝试这个：其中“sql”是查询， cursorNZ是

connMy = pyodbc.connect(DRIVER=.....)
cursorNZ = connNZ.cursor()

chunk = 10 ** 5  # tweak this
chunks = pandas.read_sql(sql, cursorNZ, chunksize=chunk)
with open('C:/test.csv', 'a') as output:
    for n, df in enumerate(chunks):
        write_header = n == 0
        df.to_csv(output, sep=';', header=write_header, na_rep='NULL')

有这个： AttributeError：'pyodbc.Cursor'对象没有属性'cursor' 有什么想法吗？

Answer 1

请勿使用cursorNZ.fetchall()。

而是直接遍历游标：

with open("c:/test.csv", "w") as archi:  # note the fixed '/'
    cursorNZ.execute(sql)
    for fila in cursorNZ:
        registro = ''
        for campo in fila:
            campo = str(campo)
            registro = registro+str(campo)+";"
        registro = registro[:-1]
        registro = registro.replace('None','NULL')
        registro = registro.replace("'NULL'","NULL")
        archi.write(registro+"\n")

就个人而言，我只会使用熊猫：

import pyodbc
import pandas

cnn = pyodbc.connect(DRIVER=.....)
chunksize = 10 ** 5  # tweak this
chunks = pandas.read_sql(sql, cnn, chunksize=chunksize)

with open('C:/test.csv', 'a') as output:
    for n, df in enumerate(chunks):
        write_header = n == 0
        df.to_csv(output, sep=';', header=write_header, na_rep='NULL')

用Python导出2Gb + SELECT到CSV（内存不足）

1 个答案: