UnboundLocalError：在 Python/Docker 中赋值之前引用的局部变量

Question

在构建 docker 容器映像后，我正在尝试运行一个简单的 Python 脚本以在本地桌面目录中打印/写入 GeoTIFF 的名称。该脚本作为独立脚本执行并生成所需的输出，但是当我尝试通过“docker run”命令运行 docker 容器映像时，我收到一个错误，指出变量是“UnboundLocalError：在分配之前引用了局部变量 'rows' ”。我不确定为什么它在运行容器但作为独立脚本运行时显示此错误。下面是我的 Dockerfile 以及脚本本身。

Dockerfile

FROM continuumio/miniconda3

ADD docker_test.py .

RUN /opt/conda/bin/conda install gdal=3.0.2

CMD [ "python", "./docker_test.py" ]

Python 脚本 (docker_test.py)

import glob
from osgeo import gdal

def image_processing():

    for file in glob.glob("*.tif"): # points to image located in the directory for parsing
        dem = gdal.Open(file)
        rows = dem.RasterYSize
        cols = dem.RasterXSize
 
  return rows, cols

rows, cols = image_processing()

with open('gdal_docker_test.txt', 'w') as f:
    f.write(f'The number of rows is: {rows}')

我觉得它应该是一个简单的修复，但我无法弄清楚调整。非常感谢任何帮助！

Answer 1

如果glob.glob("*.tif") 没有返回任何内容，则永远不会创建row 对象。

还请注意，您的版本只会返回最后一个文件的 rows, cols。

下面的修改版本有望帮助突出问题。

import glob
from osgeo import gdal

def image_processing():
    files = glob.glob("*.tif"): # points to image located in the directory for parsing

    if not files:
        raise FileNotFoundError("*.tif file not found in: {}".format(glob.glob("*")))
    else:
        for file in files:
            print(file)
            dem = gdal.Open(file)
            rows = dem.RasterYSize
            cols = dem.RasterXSize
        return rows, cols

rows, cols = image_processing()

with open('gdal_docker_test.txt', 'w') as f:
    f.write(f'The number of rows is: {rows}')

最小修改版本：

import glob
from osgeo import gdal

def image_processing():
    rows = -1
    cols = -1

    for file in glob.glob("*.tif"): # points to image located in the directory for parsing
        dem = gdal.Open(file)
        # This code is never reached in your example because the image isnt' found.
        rows = dem.RasterYSize
        cols = dem.RasterXSize
 
    return rows, cols

rows, cols = image_processing()

with open('gdal_docker_test.txt', 'w') as f:
    f.write(f'The number of rows is: {rows}')