🌐 Mailman 3 October 2020 - Python-list - python.org

Basic Python help
by mikael petterson Oct. 23, 2020

Oct. 23, 2020

Hi, I need to use the following code but in java. END_DELIM = '\n##\n' def start_delim(data_len): return '\n#%s\n' % (data_len) data = "%s%s%s" % (start_delim(len(data)), data, END_DELIM) Can anyone help me to understand what it means: I am guessing now: a function defined "start_delim" takes the length of a data string. function does modulo on something. This something I am not sure of :-) Does '\n#%s\n' will this be evaluated to a number when %s i replaced with data_len? Then the result is used as one parameter in "%s%s%s" start_delim then for the other data END_DELIM Your help is greatly appreciated! br, //mike

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Re: GUI (tkinter) popularity and job prospects for
by Lammie Jonson Oct. 23, 2020

Oct. 23, 2020

Thanks, Yes, I have some sense about how to do job interviews and market myself which is always an ongoing process. I also just have an interest in different technologies that I may want to investigate as I can get bored with certain things a little at times. If some technology seems a little interesting to me but I don't see that there are a lot of job listings for it however, then I sometimes wonder why that is etc

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Re: Dataframe to postgresql - Saving the dataframe to memory using StringIO
by Chris Angelico Oct. 22, 2020

Oct. 22, 2020

On Fri, Oct 23, 2020 at 12:15 AM Shaozhong SHI <shishaozhong(a)gmail.com> wrote: > > Thanks, Chris. > > What should I know or watch out if I decide to move from Python 2.7 to Python 3? > > What are the key issues? Syntax? > Keep it on-list please :) Key issues? Well, for starters, you don't have to worry about whether your strings are Unicode or not. They just are, unless you explicitly need them to be bytes. Syntax is probably going to be fine, since you're taking examples that were written for Python 3 anyway. There's a LOT more features in Python 3, since it's had another decade of development than Python 2 has had. Give it a try. ChrisA

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Dataframe to postgresql - Saving the dataframe to memory using StringIO
by Shaozhong SHI Oct. 22, 2020

Oct. 22, 2020

I found this last option is very interesting. Saving the dataframe to memory using StringIO https://naysan.ca/2020/06/21/pandas-to-postgresql-using-psycopg2-copy_from/ But, testing shows unicode argument expected, got 'str' Any working example for getting DataFrame into a PostgreSQL table directly? Regards, David

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Static typing—with annotations—function name & arguments, or result of call, or string
by Samuel Marks Oct. 22, 2020

Oct. 22, 2020

>From my understanding, `ast.arguments` and `inspect.Signature` are the two builtin ways of defining the function name and arguments in a structured way. What I am creating is a way of configuring… well let's be specific to my use-case. I am building a way to configure TensorFlow. One which is very type-driven, and will error as early-as-possible when incorrect types or lack of required parameters are provided. I can dynamically infer things like so: ``` import inspect import tensorflow as tf sig = inspect.signature(tf.keras.optimizers.Adam) tuple({ "default": sig.parameters[param].default, "name": param, "typ": type(sig.parameters[param].default).__name__ if sig.parameters[param].default is not inspect._empty and sig.parameters[param].annotation is inspect._empty else sig.parameters[param].annotation, } for param in sig.parameters if param != 'name' ) ``` I can also parse the docstring, as I do in my doctrans library and tool. Which will give me the options I can provide the class. So there's an obvious solution, to generate these classes: ``` class TensorFlowConfig(object): optimizer: Optional[Optimizer] = None # Or maybe a `Protocol`? class Optimizer(object): pass class AdamConfig(Optimizer): learning_rate: float = 0.001 beta_1: float = 0.9 beta_2: float = 0.999 epsilon: float = 1e-07 amsgrad: bool = False kwargs: dict = {} TensorFlowConfig().optimizer = AdamConfig() ``` But, keeping in mind the goal to expose everything in all interfaces, the question then becomes how to generate an argparse parser from this. And how to generate a function from this. And how to ensure that whatever code-completion interface one uses in Python, that it can figure out what the correct parameters are. So I should get an error about incorrect type when I: ``` # CLI --optimizer 'Adam' 'learning_rate = True' # class* TensorFlowConfig().optimizer = tf.keras.optimizers.Adam(learning_rate=True) TensorFlowConfig().optimizer = AdamConfig(learning_rate=True) # Function* MyTensorFlowClass.train(optimizer=tf.keras.optimizers.Adam(learning_rate=True)) MyTensorFlowClass.train(optimizer=AdamConfig(learning_rate=True)) * both of these next two lines—after the heading—should be equivalent ``` Syntax like this should also be valid ``` TensorFlowConfig().optimizer = 'tf.keras.optimizers.Adam' TensorFlowConfig().optimizer = 'Adam' MyTensorFlowClass.train(optimizer='tf.keras.optimizers.Adam') MyTensorFlowClass.train(optimizer='Adam') ``` Do I have huge annotations like this*, with an `Any` lopped on for further analysis down the line? - So it can easily generate into `choices` for argparse? [which will need to be subclassed in order to enable that "--optimizer 'Adam' 'learning_rate = True'" syntax] * https://github.com/SamuelMarks/ml-params-tensorflow/blob/1d48502/ml_params_… What makes sense? Thanks for your insights, Samuel Marks Charity <https://sydneyscientific.org> | consultancy <https://offscale.io> | open-source <https://github.com/offscale> | LinkedIn <https://linkedin.com/in/samuelmarks> PS: This is the `doctrans` project I referenced https://github.com/SamuelMarks/doctrans

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How to write differently to remove this type hint in Python 2.7?
by Shaozhong SHI Oct. 21, 2020

Oct. 21, 2020

Is there another way to do this? def greet(name: str) -> str: return "Hello, " + name greet File "<ipython-input-28-bee2cddf1f0d>", line 1 def greet(name: str) -> str: ^ SyntaxError: invalid syntax

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How to create a C Extension that uses CPython internals (outside limited API)?
by Marco Sulla Oct. 21, 2020

Oct. 21, 2020

I'm working on a C extension for frozendict. To make it working, I had to: 1. add by hand the whole path of dictobject.c (/home/marco/sources/cpython/Objects/dictobject.c) 2. add -DPy_BUILD_CORE 3. add the whole path of CPython includes (/home/marco/sources/cpython/Include and so on) This works on my machine, but I suspect that nobody will download the whole CPython code and add the extra CFLAGS only to make it work. What do I have to do? I have to copy the CPython source code that I need inside my c extension folder? What if I also want to support CPython from 3.6 to 3.9?

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Py_BuildValue vs PyTuple_Pack vs PyTuple_New
by Marco Sulla Oct. 20, 2020

Oct. 20, 2020

I read these three C api functions, They are similar, because they all construct a tuple[1]. IMHO, Py_BuildValue is more simple to use than PyTuple_Pack that is more simple to use than PyTuple_New. Where to use one or the other? What's the relative performance of the three functions? [1] actually, Py_BuildValue can also return non-tuple objects.

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Pickle in C does not work
by Marco Sulla Oct. 20, 2020

Oct. 20, 2020

I tried this code: static PyObject * frozendict_reduce(PyFrozenDictObject* mp, PyObject *Py_UNUSED(ignored)) { PyObject* args = PyTuple_New(1); if (args == NULL) { return NULL; } PyTuple_SET_ITEM(args, 0, (PyObject *)mp); PyObject *d = PyObject_Call((PyObject *)&PyDict_Type, args, NULL); Py_INCREF(mp); return Py_BuildValue("O(N)", Py_TYPE(mp), d); } but I get: _pickle.PicklingError: Can't pickle <class 'frozendict'>: attribute lookup frozendict on builtins failed The identical (?) Python code works: def __reduce__(self, *args, **kwargs): return (self.__class__, (dict(self), ))

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web conference on python
by Agnese Camellini Oct. 20, 2020

Oct. 20, 2020

Hello, i am not a staff member, but some connection on likeding asked me to share this link and i would be happy if it helps someone. https://python.geekle.us/?

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