En Python, un contexto (context) es una clase que implementa los m\u00e9todos ‘__enter__’ y ‘__exit__’ los cuales son llamados si la clase en llamada con la palabra reservada ‘with’. Por ejemplo, los descriptores de archivo (file handle) en Python se pueden llamar con un contexto, ahorrando llamar ‘finally’ para cerrar archivos, sin importar si hay un error.<\/p>\n
Les traigo de vuelta el programa de ‘DolarToday’ el cual escribe datos en un archivo binario, pero ahora utilizando contextos:<\/p>\n
\r\n#!\/usr\/bin\/env python3\r\n# Simple program to save the 'Dolartoday' extra official dollar rates from CSV to a custom format\r\n# Revisited to use 'contexts' to avoid using finally on exception handling\r\n# @author Jose Vicente Nunez, josevnz@kodegeek.com\r\nimport os, sys, datetime, re, gzip, struct\r\nfrom optparse import OptionParser, OptionValueError\r\nfrom datetime import datetime\r\n\r\nclass DollarToday:\r\n \r\n def __init__(self, ddate, value):\r\n if isinstance(ddate, datetime):\r\n self.__date = ddate\r\n else:\r\n self.__date = datetime.strptime(ddate, \"%m-%d-%Y\")\r\n self.__value = float(value)\r\n assert self.__value > 0.0, \"{} for date {} is invalid!\".format(value, self.__date)\r\n \r\n @property\r\n def date(self):\r\n return self.__date\r\n \r\n @date.setter\r\n def date(self, date):\r\n assert isinstance(date, datetime), \"Invalid date {}\".format(date)\r\n self.__date = date\r\n \r\n @property\r\n def value(self):\r\n return self.__value\r\n \r\n def __str__(self):\r\n return \"DollarToday[date={}, value={}]\".format(self.__date, self.__value)\r\n \r\n def __hash__(self):\r\n return str(id(self))\r\n \r\nclass DollarCollection(dict):\r\n \r\n # https:\/\/en.wikipedia.org\/wiki\/List_of_file_signatures\r\n __FILE_MAGIC = b\"DLR\\x00\"\r\n __FILE_VERSION = b\"\\x00\\x01\"\r\n __dollarStruct = struct.Struct(\" self.__FILE_VERSION:\r\n raise \"Unsupported file version: {}, expected {}\".format(version, self.__FILE_VERSION)\r\n self.clear()\r\n while True:\r\n data = fh.read(self.__dollarStruct.size)\r\n if len(data) == 0:\r\n break\r\n numbers = self.__dollarStruct.unpack(data)\r\n #if verbose:\r\n # print(\"{}\".format(\",\".join([str(x) for x in numbers])))\r\n dolar = DollarToday(\r\n datetime.fromordinal(numbers[0]),\r\n numbers[1]\r\n )\r\n self[dolar.date] = dolar\r\n except (Exception) as err:\r\n raise\r\n \r\n def readCsv(self, file):\r\n tempMap = {}\r\n try:\r\n with open(file, \"r\", encoding=\"UTF-8\") as fh:\r\n for line in fh.readlines():\r\n # 6-23-2010 9.92\r\n (date, value) = line.strip().split(\"\\t\")\r\n if re.match(\"Fecha\", date):\r\n continue\r\n try:\r\n dolVsBol = DollarToday(date, value)\r\n tempMap[dolVsBol.date] = dolVsBol\r\n except (Exception) as err:\r\n print(err)\r\n self.clear()\r\n self.update(tempMap)\r\n except (Exception) as err:\r\n raise\r\n\r\n def __str__(self):\r\n return \"Records={},\\n{}\".format(len(self), \",\\n\".join([str(date) for date in self.values()]))\r\n\r\ndef main(options):\r\n\r\n verbose = options.verbose\r\n dc = DollarCollection()\r\n if options.report == None:\r\n dc.readCsv(options.read)\r\n dc.save(options.write)\r\n else:\r\n dc.readBinary(options.report, verbose)\r\n if verbose:\r\n print(\"{}\".format(dc))\r\n\r\nif __name__ == \"__main__\":\r\n \r\n usagetext = \"\"\"\r\n%prog --read csv.file --write binary.file\r\n\r\nOr:\r\n\r\n%prog --report binary.file\r\n\r\n\"\"\"\r\n\r\n op = OptionParser(usage=usagetext)\r\n op.add_option(\r\n \"-r\", \"--read\",\r\n action=\"store\", \r\n dest=\"read\", \r\n help=\"Full path to CSV file with date,value pairs per line\")\r\n op.add_option(\r\n \"-w\", \"--write\", \r\n action=\"store\", \r\n dest=\"write\", \r\n help=\"Full path to destination file in binary format\")\r\n op.add_option(\r\n \"-p\", \"--report\", \r\n action=\"store\", \r\n dest=\"report\",\r\n help=\"Read the contents of the binary storage and generate a report. Incompatible with --read and --write\")\r\n op.add_option(\r\n \"-v\", \"--verbose\", \r\n action=\"store_true\", \r\n default=False, \r\n dest=\"verbose\", \r\n help=\"Enable verbose mode\")\r\n \r\n (options, values) = op.parse_args()\r\n\r\n main(options)\r\n<\/id><\/pre>\n","protected":false},"excerpt":{"rendered":"En Python, un contexto (context) es una clase que implementa los m\u00e9todos ‘__enter__’ y ‘__exit__’ los cuales son llamados si la clase en llamada con la palabra reservada ‘with’. Por ejemplo, los descriptores de archivo (file handle) en Python se pueden llamar con un contexto, ahorrando llamar ‘finally’ para cerrar archivos, sin importar si hay […]<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[438,239],"tags":[799,791,800,765],"_links":{"self":[{"href":"http:\/\/kodegeek.com\/blog\/wp-json\/wp\/v2\/posts\/3760"}],"collection":[{"href":"http:\/\/kodegeek.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/kodegeek.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/kodegeek.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/kodegeek.com\/blog\/wp-json\/wp\/v2\/comments?post=3760"}],"version-history":[{"count":2,"href":"http:\/\/kodegeek.com\/blog\/wp-json\/wp\/v2\/posts\/3760\/revisions"}],"predecessor-version":[{"id":3762,"href":"http:\/\/kodegeek.com\/blog\/wp-json\/wp\/v2\/posts\/3760\/revisions\/3762"}],"wp:attachment":[{"href":"http:\/\/kodegeek.com\/blog\/wp-json\/wp\/v2\/media?parent=3760"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/kodegeek.com\/blog\/wp-json\/wp\/v2\/categories?post=3760"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/kodegeek.com\/blog\/wp-json\/wp\/v2\/tags?post=3760"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}