Question

我使用psycopg2连接postgresql和python，这是我的脚本，

import sys

#set up psycopg2 environment
import psycopg2

#driving_distance module
query = """
    select *
    from driving_distance ($$
        select
            gid as id,
            start_id::int4 as source,
            end_id::int4 as target,
            shape_leng::double precision as cost
        from network
        $$, %s, %s, %s, %s
    )
"""

#make connection between python and postgresql
conn = psycopg2.connect("dbname = 'TC_routing' user = 'postgres' host = 'localhost' password = '****'")
cur = conn.cursor()

#count rows in the table
cur.execute("select count(*) from network")
result = cur.fetchone()
k = result[0] + 1

#run loops
rs = []
i = 1
while i <= k:
    cur.execute(query, (i, 1000000, False, False))
    rs.append(cur.fetchall())
    i = i + 1

h = 0
ars = []
element = list(rs)
while h <= 15:
    rp = element[0][h][2]
    ars.append(rp)
    h = h + 1

print ars
conn.close()

输出正常，

[0.0, 11810.7956476379, 16018.6818979217, 18192.3576530232, 21507.7366792666, 25819.1955059578, 26331.2523709618, 49447.0908955008, 28807.7871013087, 39670.8579371438, 42723.0239515299, 38719.7320396044, 38265.4435766971, 40744.8813155033, 43770.2158657742, 46224.8748774639]

但如果我在下面添加一些行以便将结果导出到csv文件，我就会收到此错误，

import csv

with open('test.csv', 'wb') as f:
    writer = csv.writer(f, delimiter = ',')
    for row in ars:
        writer.writerow(row)

[0.0, 11810.7956476379, 16018.6818979217, 18192.3576530232, 21507.7366792666, 25819.1955059578, 
26331.2523709618, 49447.0908955008, 28807.7871013087, 39670.8579371438, 42723.0239515299, 38719.7320396044, 38265.4435766971, 40744.8813155033, 43770.2158657742, 46224.8748774639]

Traceback (most recent call last):
  File "C:/Users/Heinz/Desktop/python_test/distMatrix_test.py", line 54, in <module>
    writer.writerow(row)
Error: sequence expected

如何解决这个问题？

我在Windows 8.1 x64下使用python 2.7.6和pyscripter。随意给我任何建议，非常感谢！

Answer 1

  import csv

  with open('test.csv', 'wb') as f:
     writer = csv.writer(f, delimiter = ',')
     for row in ars:
         writer.writerow(row)

ars只是一个列表。所以你的for循环不会从ars中提取一行。它从ars列表中获取一个元素，并尝试将其写为一行。

尝试用

替换它

     for row in ars:
         writer.writerow([row])

这会将每个元素写成csv文件中的一行。

或者如果你想在输出中有一行，那么就不要使用for循环，而是使用

   writer.writerow(ars)

Python csv错误：序列预期

1 个答案: