为什么当 pyodbc 游标在 main() 中时 "name 'cursor' is not defined"？

Question

我是运行一个 Python 程序，浓缩在下面，来自命令行，它给了我一个错误 (name 'cursor' is not defined) 并指向 cursor.fetchmany() 靠近底部的行。但是，如果我将 main() 的前两行、conn 和 cursor 赋值移动到 main() 的上方和外部，程序就会按预期运行.当我在 main() 中分配 cursor 时，为什么这不起作用？我很想知道这是否只是 pyodbc 库的一个怪癖，或者有更好的方法让它在 main() 内部工作，或者实际上可以将分配留在程序主体中.

import pyodbc
import csv
#   ...other modules...

def main():
    conn = pyodbc.connect(DSN=abcxyz, autocommit=True)
    cursor = conn.cursor()
#   ...sys.argv assignments and validation...
    pull_data(query_file, start_date, end_date, out_file)

def pull_data(query_file, start_date, end_date, out_file):
#   ...prepare query as string, date range as list...
    for date in list_dates:
        cursor.execute(query, date)
        append_rows(out_file)

def append_rows(out_file):
    with open(out_file, 'a', newline='') as file:
        writer = csv.writer(file)
        while True:
            results = cursor.fetchmany(chunk_size)
            if not results:
                break
            for result in results:
                writer.writerow(result)

if __name__ == '__main__':
    main()

Answer 1

因为 append_rows() 或 pull_data() 中未定义游标。您在 main() 中定义它，因此它只能在 main().

中访问

解决此问题的最佳方法可能是将光标对象传递给 append_rows() 和 pull_data()。

Answer 2

您收到 cursor 未定义错误的原因是因为它不存在于您的函数中。变量只存在于它们定义的范围内。

当您在 main 之外定义 cursor 时，它被声明为全局变量，这意味着它可以在脚本的所有范围内访问。

尝试：

import pyodbc
import csv
#   ...other modules...

def main():
    # Since conn and cursor are being declared here, they only exist within the scope of this function, not other functions that are called.
    conn = pyodbc.connect(DSN=abcxyz, autocommit=True)
    cursor = conn.cursor()
#   ...sys.argv assignments and validation...
    # make sure we give the cursor to pull_data so it will exist in its scope!
    pull_data(query_file, start_date, end_date, out_file, cursor)

def pull_data(query_file, start_date, end_date, out_file, cursor):
#   ...prepare query as string, date range as list...
    for date in list_dates:
        cursor.execute(query, date)
        # Pass the cursor to append_rows
        append_rows(out_file, cursor)

# cursor is actually passed to the append_rows function. Now it exists in this scope
def append_rows(out_file, cursor):
    with open(out_file, 'a', newline='') as file:
        writer = csv.writer(file)
        while True:
            results = cursor.fetchall()
            for result in results:
                writer.writerow(result)

if __name__ == '__main__':
    main()

我还建议您阅读。

为什么当 pyodbc 游标在 main() 中时 "name 'cursor' is not defined"？

Why "name 'cursor' is not defined" when pyodbc cursor is in main()?

python

pyodbc