https://jerrywang1981.github.io/tags/python/ Recent content in Python on 村边的池塘 Hugo zh-CN Tue, 09 Jun 2020 09:08:07 +0800 https://jerrywang1981.github.io/post/python/18-matplotlib-demo/ Tue, 09 Jun 2020 09:08:07 +0800 https://jerrywang1981.github.io/post/python/18-matplotlib-demo/ the code in jupyter notebook matplot_demo https://jerrywang1981.github.io/post/python/17-pandas-demo-2/ Tue, 09 Jun 2020 09:05:34 +0800 https://jerrywang1981.github.io/post/python/17-pandas-demo-2/ the code in jupyter notebook pandas_demo.ipynb https://jerrywang1981.github.io/post/python/16-pandas-demo-1/ Wed, 03 Jun 2020 16:30:03 +0800 https://jerrywang1981.github.io/post/python/16-pandas-demo-1/ the code in jupyter notebook refer to file pandas_demo.ipynb https://jerrywang1981.github.io/post/python/15-numpy-demo/ Wed, 03 Jun 2020 16:28:51 +0800 https://jerrywang1981.github.io/post/python/15-numpy-demo/ the code in jupyter notebook the file numpy_demo.ipynb https://jerrywang1981.github.io/post/python/14-anaconda/ Wed, 03 Jun 2020 16:27:28 +0800 https://jerrywang1981.github.io/post/python/14-anaconda/ How to install new package conda install xxx list env conda env list activate one env conda activate xx deactivate env conda deactivate https://jerrywang1981.github.io/post/python/13-python-context-manager/ Sun, 31 May 2020 13:58:44 +0800 https://jerrywang1981.github.io/post/python/13-python-context-manager/ python context manager use contextlib/yield @contextmanager def send_mail_context(): '''context manager with send_mail_context() ''' try: # 1 doing work BEFORE the code goes into with block print('before yield') server = smtplib.SMTP(SMTP_SERVERS[0], 25) # 2 yield back to with/caller yield server except Exception as e: print(e) finally: # 4. doing cleanup work server.quit() print('in finally') use class __enter__, __exit__ # 2 implement contextmanager with class class SMTPCT(object): ''' 1. override __enter__ __exit__ 2. in __enter__, return value ''' def __init__(self): self.smtp_server = None def __enter__(self): # 1 doing work BEFORE the code goes into with block print('in enter') self.smtp_server = smtplib.SMTP(SMTP_SERVERS[0], 25) # 2 return back to with/caller return self.smtp_server def __exit__(self, type, value, traceback): # 4. doing cleanup work print('in exit') self.smtp_server.quit() https://jerrywang1981.github.io/post/python/12-python-smtp/ Sun, 31 May 2020 13:52:03 +0800 https://jerrywang1981.github.io/post/python/12-python-smtp/ how to send mail in python #!/usr/bin/env python3 # -*- coding: utf-8 -*- # smtplib -> https://docs.python.org/3/library/smtplib.html import smtplib # contextlib -> https://docs.python.org/3/library/contextlib.html from contextlib import contextmanager # email -> https://docs.python.org/3/library/email.examples.html#email-examples from email import encoders from email.header import Header from email.mime.text import MIMEText from email.utils import parseaddr, formataddr SMTP_SERVERS = ['your smtp servers'] def _format_addr(s): ''' format the address ''' name, addr = parseaddr(s) return formataddr((Header(name, 'utf-8').encode(), addr)) def generate_mail(from_addr, to_addr, cc_addr, subject, body, mime_type='plain'): '''plain/text text/html ''' msg = MIMEText(body, mime_type, 'utf-8') msg['From'] = _format_addr(from_addr) msg['To'] = ",".join([_format_addr(x) for x in to_addr]) msg['Cc'] = ",".join([_format_addr(x) for x in cc_addr]) msg['Subject'] = Header(subject, 'utf-8').encode() return msg def send_mail(from_addr, to_addr, cc_addr, subject, body, mime_type='plain'): server = smtplib.SMTP(SMTP_SERVERS[0], 25) server.set_debuglevel(1) msg = generate_mail(from_addr, to_addr, cc_addr, subject, body, mime_type) server.sendmail(from_addr, to_addr + cc_addr, msg.as_string()) server.quit() # 1. to implement context manager, use decorator @contextmanager # and yield @contextmanager def send_mail_context(): '''context manager with send_mail_context() ''' try: # 1 doing work BEFORE the code goes into with block print('before yield') server = smtplib. https://jerrywang1981.github.io/post/python/11-python-mro/ Sun, 31 May 2020 13:50:50 +0800 https://jerrywang1981.github.io/post/python/11-python-mro/ method resolution order #!/usr/bin/env python3 # -*- coding: utf-8 -*- # method resolution order # mro class A(object): def hello(self): print('class A says hello') class B(A): pass class C(A): # class variable BP_URL = 'https://xxxxx' def __init__(self): self.name = 'ok' @staticmethod def print_hello(name, age): ''' staticmethod cannot access any class or self variabel/method ''' pass @classmethod def say(cls): '''class method can access class level variable/method ''' print(cls.BP_URL) def hello(self): print('class C says hello') class D(C, B): pass if __name__ == '__main__': d = D() d.hello() # to print the mro of one class print(d.__class__.__mro__) https://jerrywang1981.github.io/post/python/10-dunder-methods/ Sun, 31 May 2020 13:49:16 +0800 https://jerrywang1981.github.io/post/python/10-dunder-methods/ dunder methods #!/usr/bin/env python3 # -*- coding: utf-8 -*- # double underscore variable/function # dunder class A(object): def __init__(self, number): self.number = number def __eq__(self, value): ''' a == b ''' return super().__eq__(value) def __ge__(self, value): ''' a >= b ''' return super().__ge__(value) def __gt__(self, value): ''' a > b ''' return super().__gt__(value) def __le__(self, value): ''' a < b ''' return super().__le__(value) def __ne__(self, value): ''' a != b ''' return super().__ne__(value) def __str__(self): '''print(a) ''' return super().__str__() def __repr__(self): return super().__repr__() def __len__(self): ''' len(a) ''' return self.number * 10 def __lt__(self, other): '''less than a < b ''' return self.number < other.number def __getattribute__(self, name): ''' print(a[the_key]) ''' return super().__getattribute__(name) def __setattr__(self, name, value): ''' a[the_key] = 5 ''' return super().__setattr__(name, value) def __delattr__(self, name): ''' delete a['the_key'] ''' return super().__delattr__(name) if __name__ == '__main__': ''' ''' # a = A(5) # b = A(6) # print(a < b) # print(len(a)) # a['b'] = 10 # c = a['c'] pass https://jerrywang1981.github.io/post/python/09-python-decorators/ Wed, 27 May 2020 10:17:38 +0800 https://jerrywang1981.github.io/post/python/09-python-decorators/ 无参装饰器 #1. decorator without arguments def log_time_always(func): @wraps(func) def wrapped(*args, **kwargs): #1. get current time t1 = datetime.now() #2. run the function func(*args, **kwargs) #3. get current time t2 = datetime.now() print(f'in {func.__name__}, it took {t2-t1}') return wrapped 带参数的装饰器 #2. decorator with arguments, flag is True or False def log_time(flag): def wrapper(func): @wraps(func) def wrapped(*args, **kwargs): # if flag is true, we need to log the time if flag: #1. get current time t1 = datetime.now() #2. run the function func(*args, **kwargs) #3. get current time t2 = datetime.now() print(f'in {func.__name__}, it took {t2-t1}') else: func(*args, **kwargs) return wrapped return wrapper 本质 装饰器需要能够处理一个函数 无参 @decorator_1 def f(): pass 等同于 def f(): pass f = https://jerrywang1981.github.io/post/python/08-python-virtual-environment/ Tue, 19 May 2020 21:00:00 +0800 https://jerrywang1981.github.io/post/python/08-python-virtual-environment/ Details refer to offical document Virtual environment To create new virtual environment usually in folder venv python -m venv yourfoldername enter virtual environment source venv/bin/activate exit virtual environment deactivate Pip usage install package pip install packagename list installed packages pip list save installed packages to requirements.txt pip freeze > requirements.txt install packages from requirements.txt pip install -r requirements.txt https://jerrywang1981.github.io/post/python/07-python-function/ Sat, 16 May 2020 09:17:08 +0800 https://jerrywang1981.github.io/post/python/07-python-function/ 函数 #!/usr/bin/env python3 # -*- coding: utf-8 -*- # def func, snake case # return value # no args, no return def add_two_number(): print('a') # 1 arg def add_two_number_1(x): return x + 5 # return value # return multiple value def two_number_2(x, y): c = x + y d = x - y return c, d # args def add_number(x, y, *args): print(f'x = {x}') print(f'y = {y}') print(f'args = {args} ') # kwargs # def add_number_1(x, y, *args, **kwargs): print(f'x = {x}') print(f'y = {y}') # f-string f'this is string, {x}' print(f'args = {args} ') print(f'kwargs = {kwargs} ') # wrong # def add_number_2(**kwargs, *args, x, y) # pass # default def add_number_3(x, y, c=10, d = True): print(c) if __name__ == '__main__': # add_two_number() # print(add_two_number_1(6)) # print(two_number_2(10, 5)) # add_number(1,2, 3, 4, 5, 6) # add_number_1(1,2,3,4,5, https://jerrywang1981.github.io/post/python/06-condition-loop/ Sat, 16 May 2020 09:14:28 +0800 https://jerrywang1981.github.io/post/python/06-condition-loop/ 条件控制 #!/usr/bin/env python3 # -*- coding: utf-8 -*- if __name__ == '__main__': a = 5 if a > 0: print('a > 0') else: print('a < 0') if a > 0: pass elif a < 5: pass elif a < 10: pass else: pass if a > 0: if a < 5: print(a) else: print('a > 5') 循环控制 #!/usr/bin/env python3 # -*- coding: utf-8 -*- if __name__ == '__main__': # while condition a = 5 while a > 0: # print(a) a = a -1 # for in for i in range(10): print(i) # break the loop print('------------------') for i in range(10): print(i) else: # print('done') # continue the loop print('------------------') for i in range(10): if i == 5: continue print(i) count = 0 while count < 5: print (count, " 小于 5") count https://jerrywang1981.github.io/post/go/convert-pdf-to-images/ Mon, 11 May 2020 21:51:52 +0800 https://jerrywang1981.github.io/post/go/convert-pdf-to-images/ 背景 在做文字检测和文字识别的时候，有时候客户提供的是pdf格式的文件，而不是jpg/png格式，这时候就需要把pdf里面多个页面 保存成图片。 代码库pdf2image 实现 Python 参考readme docker 参考readme golang 参考readme 也可以 直接下载可执行文件直接执行 -> https://github.com/jerrywang1981/pdf2images/blob/master/pdf2image https://jerrywang1981.github.io/post/go/python-go-rpc/ Mon, 04 May 2020 00:11:12 +0800 https://jerrywang1981.github.io/post/go/python-go-rpc/ 背景 有时候，我们在python中实现了一个功能，这功能如果用golang重新写呢，会比较麻烦，如果要在golang中调用python中的功能。 方式有很多，主要就是两个程序如果沟通的问题，那方式就各种各样了，可以通过http协议，json/xml等格式，或者tcp, 当然还有个 选择就 https://jerrywang1981.github.io/post/python/class-object-method/ Sat, 02 May 2020 21:59:33 +0800 https://jerrywang1981.github.io/post/python/class-object-method/ 对象中通过类或者实例的方法调用方式的不同 如果通过类中取得的方法，需要传入实例 class A(object): def test(self, *args): print(*args) if __name__ == '__main__': a = A() a.test(7, 8, 9) # method from class object m1 = A.test m1(a, 7, 8, 9, 10) # method from instance object m2 = a.test m2(7, 8, 9, 10) 也就是说, 实例方法的第一个参数是实例本身，如果写decorator的时候，要特别注意 比如print_args这个decor https://jerrywang1981.github.io/post/python/05-Python-Dictionary/ Sat, 25 Apr 2020 18:35:30 +0800 https://jerrywang1981.github.io/post/python/05-Python-Dictionary/ Dictionary ###创建方式 a = dict() a = {} a = {'a': 1, 'b': 2} a = dict(a=1,b=2) a = [('a', 1), ('b', 2)] b = dict(a) a = zip('abc', [1,2,3]) a = { x:x*2 for x in range(10) } a = dict.fromkeys(range(3), 'y') https://jerrywang1981.github.io/post/python/04-python-tuple/ Fri, 24 Apr 2020 21:54:58 +0800 https://jerrywang1981.github.io/post/python/04-python-tuple/ Tuple Python 的元组与列表类似，不同之处在于元组的元素不能修改。 不可变 空元组, 一个元素元组 元组运算 元组在参数中的应用 创建tuple的方式 https://jerrywang1981.github.io/post/python/03-python-list/ Fri, 24 Apr 2020 21:05:59 +0800 https://jerrywang1981.github.io/post/python/03-python-list/ 列表 序列是Python中最基本的数据结构。序列中的每个元素都分配一个数字 - 它的位置，或索引，第一个索引是0，第二个索引是1，依此类推 索引访问 长度 空或者False 创建列表的方式 a = [] a = [1,2,3] a = list() a = list('abcdefg') a = list(range(10)) a = [ x for x in range(20) ] append In [17]: a=[1,2,3] In [18]: a.append(4) In [19]: a Out[19]: [1, 2, 3, 4] In [20]: extend In [21]: a Out[21]: [1, 2, 3, 4] In [22]: a.extend([5,6]) https://jerrywang1981.github.io/post/python/02-python-variable/ Thu, 23 Apr 2020 14:23:52 +0800 https://jerrywang1981.github.io/post/python/02-python-variable/ 变量 命名 变量名必须是大小写英文、数字和_的组合，且不能用数字开头 允许的变量名：a, a1, B_5, ____5, _C 静态语言，动态语言 大小写敏感 Dunder 规范 snake_case e.g. a_b, total_count 变量 函数名 模块 包 CamelCase e.g. Person, TeamMember 类名 常量 一般用大写, PI=3.14 https://jerrywang1981.github.io/post/python/01-python-data-type/ Thu, 23 Apr 2020 13:51:39 +0800 https://jerrywang1981.github.io/post/python/01-python-data-type/ 基本数据类型 整数 int 十进制： -1, 0, 1000, -8000, 88 八进制：0o10, 0o27 十六进制：0x10, 0xff 数学运算 + - * / // % 浮点数 float 比如：1.23, 2.6e3 字符串 str 字符串是以单引号’或双引号"括起来的任意文本 如果字符串内部包含’,", 可以用转义字符\来标识 转义 \ 不转义 https://jerrywang1981.github.io/post/python/python-nest/ Sat, 11 Apr 2020 21:15:14 +0800 https://jerrywang1981.github.io/post/python/python-nest/ 背景 最近有做一个nestjs的项目，用的nestjs实现的微服务，如果所有的功能都用node/nestjs写，那倒也没有什么问题了。可是有一个功能是需要用到机器学习，代码是用python写的，需要用python实现一个微服务，供nest app来调用，同时，python代码也需要调