Python Features

Genearl Concept

What is .pyd

.pyd files are DLL’s, but there are a few differences.

If you have a DLL named foo.pyd, then it must have a function initfoo(). You can import this dll in Python

import foo

Python will search for foo.pyd (as well as foo.py, foo.pyc) and if it finds this pyd, Python will attempt to call initfoo() to initialize it. You do not link your .exe with foo.lib, as that would cause Windows to require the DLL to be present. Note that the search path for foo.pyd is PYTHONPATH, not the same as the path that Windows uses to search for foo.dll. Also, foo.pyd need not be present to run your program, whereas if you linked your program with a dll, the dll is required. Of course, foo.pyd is required if you want to say import foo. In a DLL, linkage is declared in the source code with __declspec(dllexport). In a .pyd, linkage is defined in a list of available functions.

Python Property Define

class Student:
    def __init__(self):
        self._score = None

    def get_score(self):
        return self._score

    def set_score(self, value):
        self._score = value

    def del_score(self):
        del self._score

    score = property(get_score, set_score, del_score, "doc")


class Student:
    def __init__(self):
        self._score = None

    @property
    def score(self):
        """doc"""
        return self._score

    @score.setter
    def set_score(self, value):
        self._score = value

    @score.deleter
    def del_score(self):
        del self._score

Partial Function

Partial

import functools
int2 = functools.partial(int, base=2)

Wraps

import time
from functools import wraps
 
def timethis(func):
    @wraps(func)
    def wrapper(*args, **kwargs):
        start = time.time()
        result = func(*args, **kwargs)
        end = time.time()
        print(func.__name__, end-start)
        return result
    return wrapper

Built-in Variables

globals()

Return a dictionary representing the current global symbol table. This is always the dictionary of the current module (inside a function or method, this is the module where it is defined, not the module from which it is called.

hash(object)

Return the hash value of the object (if it has one). Hash values are integers. They are used to quickly compare dictionary keys during a dictionary lookup. Numeric values that compare equal have the same hash value (even if they are of different types, as is the case for 1 and 1.0).

IPDB

import pdb;pdb.settrace();

n[ext] n simply continues program execution to the next line in the current function. This will be your most-typed command. s[tep] s steps to the very next line of executable code, whether it’s inside a called method or just on the next line. I think of this as “step into” for tunneling into a function or method. c[ontinue] c continues program execution until another breakpoint is hit. l[ist] [first[, last]] l lists a larger portion of code–11 lines–moving down the file with successive calls. You can optionally provide a line number to center the view on, as well as a second number for a range. p[rint] and pp p and pp are print and pretty-print. pp uses the pprint module. I use pp almost exclusively. a[rgs] a is one of my favorites. It prints out all the arguments the current function received. j[ump] line_number j will jump to the given line of code, actually skipping the execution of anything between.

Tips for effective pdb use

• pp locals()and pp globals() Use these commands to see all variables in the given scope, local or global. This is super useful for a quick glance at all the objects your program has access to at that moment.

• Change variables You can change the value of variables while stepping through your code.

• Use tab completion and introspection This is specific to ipdb users, since pdb doesn’t have this functionality.

Python File Operation

Retrive Infomartion

import os
 
path = r'D:\Data\1.txt'
# Get the last component of the path
os.path.basename(path)
# Get the directory name
os.path.dirname(path)
# Split the file extension
os.path.splitext(path)
 
# *******************************************************************
# Testing for the Existence of a File
os.path.exists(r'D:\1.txt')
# Is a regular file
os.path.isfile(path)
# Is a directory
os.path.isdir(path)
 
# get file/folder property
os.path.getsize(path)
os.path.getmtime(path)

import time
time.ctime(os.path.getmtime(path))
 
# *******************************************************************
# Getting a Directory Listing
folder = r'D:\data'
import os
names = os.listdir(folder)
# Get all regular files
names = [name for name in os.listdir(folder)if os.path.isfile(os.path.join(folder, name))]
# Get all dirs
dirnames = [name for name in os.listdir(folder) if os.path.isdir(os.path.join(folder, name))]

Create

path = r'D:\1\2\3'
filename = r'D:\1\2\3\1.txt'
# make subdirs
os.makedirs(path)
# remove dir
os.rmdir(path)
# remove files
os.remove(filename)
# rename file
os.rename(oldfilename, newfilename)

Shutil

# copyfile oldfile and newfile must be file
shutil.copyfile("oldfile","newfile")
# copyfile or dir 
# oldfile and newfile can be file or dir 
shutil.copy("oldfile","newfile")          
# copy dir
# old dir and new dir muse be dir cannot be file, and new dir cannot be exsit
shutil.copytree("olddir","newdir")        
# raname dir or file
os.rename("oldname","newname")  
# move dir or file
shutil.move("oldpos","newpos")   
# delete dir or file
os.remove("file")
# can delete empty dir
os.rmdir("dir")

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