如何将列表保存到文本文件？

Question

我想将所有 x ad y 坐标（将栅格图层中的每个像素居中）保存为文本文件中的列表。首先为了测试，我在下面写了正确的代码：

import os
import pickle

mylist = [(12, 25), (65, 96), (10, 15)]

path = r"data/listfile"

file = 'file.txt'

if not os.path.exists(path):
    os.makedirs(path)


with open(os.path.join(path, file), 'wb') as handle:
    pickle.dump(mylist, handle)

with open(os.path.join(path, file), 'rb') as handle:
    aa = pickle.loads(handle.read())
print aa

在下一步中，我将此代码实际用于我的栅格图层。该代码的 MCVE 是：

from qgis.core import *
from PyQt4 import *
import os
import pickle

ds = QgsRasterLayer("/LData/Pop/lorst.tif", "Raster")

pixelWidth = ds.rasterUnitsPerPixelX()
pixelHeight = ds.rasterUnitsPerPixelY()
originX, originY = (ext.xMinimum(), ext.yMinimum())
src_cols = ds.width()
src_rows = ds.height()

path = r"LData/Pop"

file = 'List.txt'

if not os.path.exists(path):
    os.makedirs(path)


def pixel2coord(x, y):
    xp = (pixelWidth * x) + originX + (pixelWidth / 2)
    yp = (pixelHeight * y) + originY + (pixelHeight / 2)
    return QgsPoint(xp, yp)

list =[]

for i in range(0, src_cols):
    for j in range(0, src_rows):
        rspnt = pixel2coord(i, j)
        list.append(rspnt)

with open(os.path.join(path, file), 'wb') as handle:
    pickle.dump(list, handle)

with open(os.path.join(path, file), 'rb') as handle:
    lst = pickle.loads(handle.read())

但是我收到了这个错误：

Traceback (most recent call last):
  File "<input>", line 1, in <module>
  File "/tmp/tmp4rPKQ_.py", line 70, in <module>
    pickle.dump(pntRstList, handle)
  File "/usr/lib/python2.7/pickle.py", line 1376, in dump
    Pickler(file, protocol).dump(obj)
  File "/usr/lib/python2.7/pickle.py", line 224, in dump
    self.save(obj)
  File "/usr/lib/python2.7/pickle.py", line 286, in save
    f(self, obj) # Call unbound method with explicit self
  File "/usr/lib/python2.7/pickle.py", line 606, in save_list
    self._batch_appends(iter(obj))
  File "/usr/lib/python2.7/pickle.py", line 621, in _batch_appends
    save(x)
  File "/usr/lib/python2.7/pickle.py", line 306, in save
    rv = reduce(self.proto)
  File "/usr/lib/python2.7/copy_reg.py", line 71, in _reduce_ex
    state = base(self)
TypeError: the sip.wrapper type cannot be instantiated or sub-classed

有什么方法可以将 xy 列表转换为文本文件并以数字格式而不是 str 格式读取它？

Answer 1

最简单的方法是放弃使用 QgsPoint(xp, yp) 并改用元组，即 (xp, yp)。 QgsPoint 似乎是 C++ class 的 SIP 包装器；和 SIP 包装器不会知道酸洗。

还要注意 pyqgis documentation 是这样说的：

Note

The tuples (x,y) are not real tuples, they are QgsPoint objects, the values are accessible with x() and y() methods.

它们看起来像元组，但它们一点也不像元组，您甚至无法使用 t[0].

访问单个坐标

也就是说，您可以使用

轻松地将此类点的列表转换为元组列表

lst = [(p.x(), p.y()) for p in lst]
pickle.dump(lst, handle)

如何将列表保存到文本文件？

How to save a list to a text file?

cpython

list

pickle

qgis

python-2.7