Saving Data
Learn how to save and load NumPy data.
We'll cover the following
Chapter Goals:
- Learn how to save and load data in NumPy
- Write code to save NumPy data to a file
A. Saving
After performing data manipulation with NumPy, it's a good idea to save the data in a file for future use. To do this, we use the np.save function.
The first argument for the function is the name/path of the file we want to save our data to. The file name/path should have a ".npy" extension. If it does not, then np.save will append the ".npy" extension to it.
The second argument for np.save is the NumPy data we want to save. The function has no return value. Also, the format of the ".npy" files when viewed with a text editor is largely gibberish when viewed with a text editor.
If np.save is called with the name of a file that already exists, it will overwrite the previous file.
The code below shows examples of saving NumPy data.
arr = np.array([1, 2, 3])# Saves to 'arr.npy'np.save('arr.npy', arr)# Also saves to 'arr.npy'np.save('arr', arr)
B. Loading
After saving our data, we can load it again using np.load. The function's required argument is the file name/path that contains the saved data. It returns the NumPy data exactly as it was saved.
Note that np.load will not append the ".npy" extension to the file name/path if it is not there.
The code below shows how to use np.load to load NumPy data.
arr = np.array([1, 2, 3])np.save('arr.npy', arr)load_arr = np.load('arr.npy')print(repr(load_arr))# Will result in a FileNotFoundError: If we uncomment line 7 and run again.#load_arr = np.load('arr')
Time to Code!
The coding exercise in this chapter will require you to complete the save_points function, which will save some randomly generated 2-D points in a file.
You'll generate 100 (x, y) points from a uniform distribution in the range [-2.5, 2.5), then save the points to save_file.
Set points equal to np.random.uniform, with the low and high keyword arguments representing the lower and upper ends of the range. The size keyword argument should be set to (100, 2).
Call np.save with save_file as the first argument and points as the second argument.
def save_points(save_file):# CODE HEREpass
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