Category: Python Answers

Sometimes, we want to fix ValueError: setting an array element with a sequence with Python NumPy.

In this article, we’ll look at how to fix ValueError: setting an array element with a sequence with Python NumPy.

How to fix ValueError: setting an array element with a sequence with Python NumPy?

To fix ValueError: setting an array element with a sequence with Python NumPy, we call numpy.array with a dtype that can be used for holding the objects in the list that we called array with.

For instance, we write

a = numpy.array([1.2, "abc"], dtype=object)

to call numpy.array with a list and the dtype argument set to object so that NumPy can return an array with a type that can be cast for all objects in the list.

Conclusion

To fix ValueError: setting an array element with a sequence with Python NumPy, we call numpy.array with a dtype that can be used for holding the objects in the list that we called array with.

Sometimes, we want to import csv to list with Python.

In this article, we’ll look at how to import csv to list with Python.

How to import csv to list with Python?

To import csv to list with Python, we can use the csv module.

For instance, we write

import csv

with open('file.csv', newline='') as f:
    reader = csv.reader(f)
    data = list(reader)

print(data)

to call open to open the file csv.file.

Then we call csv.reader with file f to read the file.

And then we call list on the reader iterator to convert the read csv contents into a list.

Conclusion

To import csv to list with Python, we can use the csv module.

Sometimes, we want to crop an image in OpenCV using Python.

In this article, we’ll look at how to crop an image in OpenCV using Python.

How to crop an image in OpenCV using Python?

To crop an image in OpenCV using Python, we can slice the image list.

For instance, we write

import cv2
img = cv2.imread("lenna.png")
crop_img = img[y:y+h, x:x+w]
cv2.imshow("cropped", crop_img)
cv2.waitKey(0)

to open the image with

cv2.imread("lenna.png")

Then we crop the image by slicing the pixels with

crop_img = img[y:y+h, x:x+w]

Next we shouw the cropped image with imshow.

Conclusion

To crop an image in OpenCV using Python, we can slice the image list.

Sometimes, we want to write to an Excel spreadsheet with Python.

In this article, we’ll look at how to write to an Excel spreadsheet with Python.

How to write to an Excel spreadsheet with Python?

To write to an Excel spreadsheet with Python, we can use Pandas.

For instance, we write

from pandas import DataFrame

l1 = [1, 2, 3, 4]
l2 = [1, 2, 3, 4]
df = DataFrame({"Stimulus Time": l1, "Reaction Time": l2})
df.to_excel("test.xlsx", sheet_name="sheet1", index=False)

to create a data frame with the DataFrame class called with a dict.

Then we call to_excel on the df data frame with the file name to write to, the sheet_name, and index set to False to not write the index column to the sheet.

The dict keys are the headers in sheet1 and the list values are the columns.

Conclusion

To write to an Excel spreadsheet with Python, we can use Pandas.

Sometimes, we want to duplicate sys.stdout to a log file with Python.

In this article, we’ll look at how to duplicate sys.stdout to a log file with Python.

How to duplicate sys.stdout to a log file with Python?

To duplicate sys.stdout to a log file with Python, we can create our own logger class.

For instance, we write

import sys

class Logger(object):
    def __init__(self):
        self.terminal = sys.stdout
        self.log = open("log.dat", "a")

    def write(self, message):
        self.terminal.write(message)
        self.log.write(message)  

sys.stdout = Logger()

print("%d %d" % (1, 2))

to create the Loffer class that has the write method to write message to the terminal with self.terminal.write.

And we write message to the log file with self.log.write.

Then we set sys.stdout to a Logger instance.

Now when we call print, the argument’s value should be printed to the screen and appended to the log.

Conclusion

To duplicate sys.stdout to a log file with Python, we can create our own logger class.