We've been working in our separate code files, sometimes importing code. Now we'll focus on getting data both to and from external files
\n","We'll start with a few simple examples where we write names into a document and the read them line by line"]},{"cell_type":"code","execution_count":2,"id":"c913485b","metadata":{},"outputs":[],"source":["#Writing in an external file, simples form\n","name = input(\"Name: \")\n","#The 'w' meens we're open for writing (overwriting old stuff)\n","file = open(\"names.txt\", \"w\")\n","file.write(name)\n","file.close()"]},{"cell_type":"markdown","id":"11675f5c","metadata":{},"source":["When we do this we either open the named file overwriting the content with a new line, or we create a new document and add the new line.\n","If we instead use \"a\", we can append instead of overwrite"]},{"cell_type":"code","execution_count":5,"id":"bfef8e9a","metadata":{},"outputs":[],"source":["#Writing in an external file, simplest form\n","name = input(\"Name: \")\n","#The 'a' meens we're open for appending\n","file = open(\"names.txt\", \"a\")\n","file.write(f\"{name}\\n\")\n","file.close()"]},{"cell_type":"markdown","id":"08c86e00","metadata":{},"source":["If we run this twice we get 2 separate lines with our names:\n","with\n"]},{"cell_type":"code","execution_count":null,"id":"ee34385d","metadata":{},"outputs":[],"source":["#Writing using with, opens and closes automatically\n","name = input(\"Name: \")\n","with open(\"names.txt\", \"a\") as file:\n"," file.write(f\"{name}\\n\")"]},{"cell_type":"code","execution_count":6,"id":"d1b406e9","metadata":{},"outputs":[{"name":"stdout","output_type":"stream","text":["hello, Kurre\n","hello, Pelle\n"]}],"source":["#Reading using with and creating list, stripping whitespace we don't need\n","names = []\n","with open(\"names.txt\") as file:\n"," for line in file:\n"," names.append(line.rstrip())\n","\n","for name in sorted(names):\n"," print(f\"hello, {name}\")"]},{"cell_type":"markdown","id":"f036685d","metadata":{},"source":["This is great, but sometimes we need to have a bit more structure. We could use JSON, but just for fun, lets go with another really common format.
\n","CSV"]},{"cell_type":"code","execution_count":3,"id":"49d8507f","metadata":{},"outputs":[{"name":"stdout","output_type":"stream","text":["Anders is in Sweden\n","Ben is in Netherlands\n","Einstein is in Germany\n","Leto is in Belgium\n","Name is in Country\n","Samuel is in Sweden\n","Virul is in Sri Lanka\n"]}],"source":["#Read from our csv-file, creating list, sorting and displaying\n","students = []\n","\n","with open(\"students.csv\") as file:\n"," for line in file:\n"," name, land = line.rstrip().split(\",\")\n"," students.append(f\"{name} is in {land}\")\n","\n","for student in sorted(students):\n"," print(student)"]},{"cell_type":"code","execution_count":4,"id":"b55567e4","metadata":{},"outputs":[{"name":"stdout","output_type":"stream","text":["Ben is in Netherlands\n","Samuel is in Sweden\n","Anders is in Sweden\n","Leto is in Belgium\n","Virul is in Sri Lanka\n","Einstein is in \"Germany West\"\n"]}],"source":["#If we instead want to save the students as small dictionaries\n","students = []\n","with open(\"students.csv\") as file:\n"," for line in file:\n"," name, land = line.rstrip().split(\",\")\n"," student = {\"name\": name, \"land\": land}\n"," students.append(student)\n","\n","for student in students:\n"," print(f\"{student['name']} is in {student['land']}\")"]},{"cell_type":"markdown","id":"04cb42a6","metadata":{},"source":["But these aren't sorted... lets fix this by implementing a search-fix"]},{"cell_type":"code","execution_count":5,"id":"ba8cf41e","metadata":{},"outputs":[{"name":"stdout","output_type":"stream","text":["Anders is in Sweden\n","Ben is in Netherlands\n","Einstein is in \"Germany West\"\n","Leto is in Belgium\n","Samuel is in Sweden\n","Virul is in Sri Lanka\n"]}],"source":["students = []\n","\n","with open(\"students.csv\") as file:\n"," for line in file:\n"," name, land = line.rstrip().split(\",\")\n"," students.append({\"name\": name, \"land\": land})\n","\n","\n","def get_name(student):\n"," return student[\"name\"]\n","\n","\n","for student in sorted(students, key=get_name):\n"," print(f\"{student['name']} is in {student['land']}\")"]},{"cell_type":"markdown","id":"07cd065a","metadata":{},"source":["This can be even further improved. We don't need to have a separate function, we can use the generic term lambda"]},{"cell_type":"code","execution_count":4,"id":"f3b243ab","metadata":{},"outputs":[{"ename":"ValueError","evalue":"too many values to unpack (expected 2)","output_type":"error","traceback":["\u001b[0;31m---------------------------------------------------------------------------\u001b[0m","\u001b[0;31mValueError\u001b[0m Traceback (most recent call last)","\u001b[1;32m/Users/randlerm2/Documents/UU och Campus/Undervisning UU/Kurser 23-24/23 Coding in Python /Lectures/L7/files-i-o.ipynb Cell 14\u001b[0m line \u001b[0;36m5\n\u001b[1;32m 3\u001b[0m \u001b[39mwith\u001b[39;00m \u001b[39mopen\u001b[39m(\u001b[39m\"\u001b[39m\u001b[39mstudents2.csv\u001b[39m\u001b[39m\"\u001b[39m) \u001b[39mas\u001b[39;00m file:\n\u001b[1;32m 4\u001b[0m \u001b[39mfor\u001b[39;00m line \u001b[39min\u001b[39;00m file:\n\u001b[0;32m----> 5\u001b[0m name, land \u001b[39m=\u001b[39m line\u001b[39m.\u001b[39mrstrip()\u001b[39m.\u001b[39msplit(\u001b[39m\"\u001b[39m\u001b[39m,\u001b[39m\u001b[39m\"\u001b[39m)\n\u001b[1;32m 6\u001b[0m students\u001b[39m.\u001b[39mappend({\u001b[39m\"\u001b[39m\u001b[39mname\u001b[39m\u001b[39m\"\u001b[39m: name, \u001b[39m\"\u001b[39m\u001b[39mland\u001b[39m\u001b[39m\"\u001b[39m: land})\n\u001b[1;32m 8\u001b[0m \u001b[39mfor\u001b[39;00m student \u001b[39min\u001b[39;00m \u001b[39msorted\u001b[39m(students, key\u001b[39m=\u001b[39m\u001b[39mlambda\u001b[39;00m student: student[\u001b[39m\"\u001b[39m\u001b[39mname\u001b[39m\u001b[39m\"\u001b[39m]):\n","\u001b[0;31mValueError\u001b[0m: too many values to unpack (expected 2)"]}],"source":["students = []\n","\n","with open(\"students2.csv\") as file:\n"," for line in file:\n"," name, land = line.rstrip().split(\",\")\n"," students.append({\"name\": name, \"land\": land})\n","\n","for student in sorted(students, key=lambda student: student[\"name\"]):\n"," print(f\"{student['name']} is in {student['land']}\")"]},{"cell_type":"markdown","id":"fbbdff31","metadata":{},"source":["Lets add a line to our csv that has 2 commas..., this will of course generate an error.\n","We'll fix this by once again leaning on a library\n","DictReader"]},{"cell_type":"code","execution_count":6,"id":"bc31b713","metadata":{},"outputs":[{"name":"stdout","output_type":"stream","text":["Anders is in Sweden\n","Ben is in Netherlands\n","Einstein is in Germany,West\n","Leto is in Belgium\n","Samuel is in Sweden\n","Virul is in Sri Lanka\n"]}],"source":["import csv\n","\n","students = []\n","\n","with open(\"students2.csv\") as file:\n"," reader = csv.DictReader(file)\n"," for row in reader:\n"," students.append({\"name\": row[\"name\"], \"land\": row[\"land\"]})\n","\n","for student in sorted(students, key=lambda student: student[\"name\"]):\n"," print(f\"{student['name']} is in {student['land']}\")"]},{"cell_type":"markdown","id":"62d3a2cf","metadata":{},"source":["Ok, but what about writing using the CSV-module?"]},{"cell_type":"code","execution_count":20,"id":"8b3ac045","metadata":{},"outputs":[],"source":["import csv\n","students = []\n","while True:\n"," try:\n"," name = input(\"What's your name? \")\n"," land = input(\"What's your home country? \")\n"," students.append({\"name\":name,\"land\":land})\n"," except EOFError:\n"," break\n","\n","with open(\"students4.csv\", \"a\") as file:\n"," writer = csv.DictWriter(file, fieldnames=[\"name\", \"land\"])\n"," for student in students:\n"," writer.writerow({\"name\": student[\"name\"], \"land\":student[\"land\"]})"]}],"metadata":{"kernelspec":{"display_name":"Python 3","language":"python","name":"python3"},"language_info":{"codemirror_mode":{"name":"ipython","version":3},"file_extension":".py","mimetype":"text/x-python","name":"python","nbconvert_exporter":"python","pygments_lexer":"ipython3","version":"3.11.4"}},"nbformat":4,"nbformat_minor":5}