Non-Java Language

implicit parameter -> using variables explicitly passed-in parameters will be passed like this: foo(using someVariable) implicit variables -> given variables implicit class -> extension Pureconfig com.github.pureconfig:pureconfig_2.13 -> com.github.pureconfig:pureconfig-generic-scala3_3 implicit def hint[T] = … -> given [T]: ProductHint[T] = … Add given ConfigReader[MyConf] = deriveReader Mockito remove org.mockito:mockito-scala because it doesn’t support scala3 mock[SomeClass] -> mock(classOf[SomeClass]) …

A list of things I changed in a Scala 2->3 upgrade Read More »

Instead it’s based on position. To be specific, the first column in the select sql will be mapped to the first property of the case class. Here is an example: Let’s say in the db there is a table called foo_bar foo bar fff bbb This is not desirable. But the author of Doobie won’t …

Note: Doobie’s row->case class mapping is not based on case class property name Read More »

It’s said IO.pure() means eager evaluation. But it doesn’t seem to so in this example: Here println(“print in pure”) is executed just like as if it’s IO.apply() Another example, however, discloses the truth Here is it how it works: When printTwice() is called, every expression inside it is evaluated IO.apply(println(“print in lazy”)) is evaluated as …

In Cats-effect, when is xxx inside IO.pure(xxx) executed? Read More »

You’ve tried thumbnail(), resize(), save(quality=20),  but you still get an image too big? Maybe it’s because you are generating a PNG file.  Change it to JPG and you will get a much smaller file ! It’s because PNG format is a lossless compression file format.  Without losing quality you can’t get a considerably small image …

Python: PIL generates an image too big? Read More »

You’ve created a new column and you want set its value as the "id" column. What to do?  Add the following line to the generated migration file or you can create new migration file migrations.RunSQL(sql=”update some_table set new_column = id”)

Don’t try to be smart.  You must   1. Manually convert query sets to dicts  2. Convert the dicts to JSON   Other approaches that convert query sets directly to JSON are not robust.  

Problem:    1. A task has a top-level variable, whose value is 1 at first  2. After run once by celery, the value is changed to 2   3. When running task with celery for the second time, you will see the value is still 1 ! That’s because the the worker running for the first …

Keep in mind that celery workers don’t share global states Read More »

There is requirement for a method to get things of a man.  Where to put it?   man.get_things() or   (static) Thing.get_things_by_man()  ?   From OO’s perspective, the former sounds more natural.   I was planning to adopt this approach until I found a problem:  it may lead to duplicate db access code because not …

man.get_things() or Thing.get_things_by_man() when Active Records Pattern is used? Read More »

  Celery worker’s –autoreload option seems not working for a lot of people, especially those who use OS X.   I wrote a python script to start celery worker and monitor the changes in code to reload celery worker if there is any chagne. Check it out here. 

According to my test, they are stateful objects. Reusing a single instance will lead to wrong results.  Every time you encrypt or decrypt anything, you should create a new cipher, such as  cipher = DES3.new(some_key, DES3.MODE_CFB, iv)