Category Archives: develope

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

      No Comments on Some tips for opencv-python

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 »

Write text to file with disabling buffer in Python3

In Python2 era, we could use these code to write the file without buffer:

But in Python3 we can only write binary file by disabling buffer:

The only way to write text file without buffering is:

Adding ‘flush()’ everywhere is a terrible experience for a programmer who… Read more »

Some tips about python this week

List of lists in python Created a list of lists by using multiply symbol:

It’s weird that adding one item to first list have side-effect on second list! Seems ‘* 2’ makes two reference for one list. How to avoid this then? The answer is using normal syntax:

Read more »

How could it possible to assign an integer to string?

The snippet below could be compiled and run:

The result is:

I noticed that the corresponding value of key ‘banana’ is empty. The reason is I assign an integer directly to key ‘banana’ by mistake. But how could c++ compiler allow me to do this? Why doesn’t it… Read more »

Move semantics in C++11

      No Comments on Move semantics in C++11

After studying an example for Move Semantics of C++11, I write a more complete code snippet:

Pay attention to last two lines in ‘move constructor’:

Since ‘move constructor’ will not set initial value for m_size and m_data of ‘v4’, the m_size and m_data of ‘v3’ will be uninitial… Read more »

Use pandas and matplotlib to draw line chart

I have two CSV files. Their content looks like:

The simplest way to load and draw them is by using pandas and matplotlib.

The figure draw out by this snippet is shown below: