Sequence data types in Python
Institute for Environmental and Spatial Analysis...University of North Georgia
Contents
1 Tuples
Tuples are array-like immutable objects.
Immutable objects cannot be modified once defined.
Elements are accessed using a 0-based index.
x = (1, 2.3, '4', [10, 20]) # create a tuple with different data types
len(x) # tuple size
x[0] # first element
x[0] = 10 # try to modify it
x[3][0] # 2-dimensional indexing
x[3][0] = 1 # works?2 Lists
Lists are array-like mutable objects.
Mutable objects can be modified.
Elements are accessed using a 0-based index.
x = [1, 2.3, '4', (10, 20)] # create a list with different data types
len(x) # list size
x[0] # first element
x[0] = 10 # try to modify it
x[3][0] # 2-dimensional indexing
x[3][0] = 1 # works?3 Slicing array-like objects
Slicing array-like objects is not any different from slicing strings.
Use the same slicing method to access individual elements in an array-like object.
4 Exercise: Read a GeoTIFF file as a NumPy array using GDAL
- Download elevation.tif.
- Start a new JupyterLab notebook.
- Learn about the GDAL and NumPy modules.
- Try this code line by line.
- Check this article for more explanations.
# we'll use the gdal module
from osgeo import gdal
# read in elevation.tif as a GDAL dataset object; of course, use your path to
# elevation.tif; it'll lock elevation.tif
ds = gdal.Open('p:/tmp/elevation.tif')
type(ds)
# see the list of attributes
dir(ds)
# let's see how many bands we have in elevation.tif
ds.RasterCount
# get the first and only band; note here that band numbering is 1-based
band = ds.GetRasterBand(1)
type(band)
# read the band as a NumPy array
arr = band.ReadAsArray()
type(arr)
# now, release elevation.tif; no more access to ds and band
del ds, band
# what is its dimension?
arr.shape5 Exercise: Read a GeoTIFF file as a NumPy array using ArcPy
- Download elevation.tif.
- Open ArcGIS Pro with no templates.
- Open the Python window: View ⇒ Python
- Learn about the NumPy module.
# read in elevation.tif as a Raster object; of course, use your path to
# elevation.tif; it'll lock elevation.tif
ras = arcpy.Raster('p:/tmp/elevation.tif')
type(ras)
# type ras + <dot> and see the list of attributes
# ras.
# let's see how many bands we have in elevation.tif
ras.bandCount
# read the band as a NumPy array
arr = arcpy.RasterToNumPyArray(ras)
type(arr)
# now, release elevation.tif; no more access to ras
del ras
# what is its dimension?
arr.shape6 Exercise: List and indexing
Let’s see how we can access individual elements in a list.
A = [12, 34, 45, 67]
print(A[0])
print(A[3])