Category Archives: develope

Be careful of the ternary operator in Python

The result will be:

Where is the last go? It goes with the no. The python interpreter will consider "no" / "last" under the else condition even it actually break the syntax rule. The correct way to write the ternary operator should be:

Now the result become:… Read more »

To construct DataFrame more effectively

The old code of python looks like:

This snippet above will cost 7 seconds to run on my laptop. Actually, pd.concat() is an expensive operation for CPU. So let’s replace it with common python dictionary:

This snippet only costs 0.03 seconds, which is more effective.

Tips about pytest

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1. Error for “fixture ‘mocker’ not found” After running pytest, it reported:

The solution is just installing the missing pip package:

2. How to make sure a function has been called without caring about its arguments? There are two methods. The first method is using “.called”

The… Read more »

The generating speed for random number in Python3

Just want to generate random number in a range (no matter float or integer) by using Python. Since I only need to get a random number in my code once a time, the speed for calling the generating-function is critical. So let’s do the experiment:

The result is:

Read more »

The weird comparison behaviours of Python string

A part of my code didn’t work well, as below:

It will not print out anything totally. So I directly printed out the actually value of mapping[‘colour’]:

Why ‘Red’ is not ‘Red’? After changed the judgement from ‘is’ to ‘==’, the result became correct. The key is that… Read more »

Tips about Numpy and PyTorch

1. Type convertion in Numpy Here is my code:

Guess what? The type of variable ‘c’ is ‘float64’! Seems Numpy automatically considers a empty array of Python as ‘float64’ type. So the correct code should be:

This time, the type of ‘c’ is ‘int64’ 2. Convert a tensor… Read more »

Some tips for opencv-python

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Type conversion Using opencv-python to add object-detection rectangle for the image:

The result looks like this But in a more complicated program, I processed a image from float32 type. Therefore the code looks like:

But this time, the rectangle disappeared. The reason is opencv-python use numpy array for… Read more »

Get the type of engine for a table in MySQL

To view show the type of engine a MySQL table used, we could type:

Although the command is simple, the output is too much. We could also use a slightly more complicated command to output briefly:

Some tips about Python, Pandas, and Tensorflow

There are some useful tips for using Keras and Tensorflow to build models. 1. Using applications.inception_v3.InceptionV3(include_top = False, weights = ‘Imagenet’) to get pretrained parameters for InceptionV3 model, the console reported:

The solution is here. Just install some packages:

2. Could we use ‘add’ to merge two DataFrames… Read more »