{"id":1031,"date":"2016-02-16T15:17:44","date_gmt":"2016-02-16T15:17:44","guid":{"rendered":"https:\/\/blogs.glowscotland.org.uk\/nl\/ColtnessHS-ComputingScience\/?p=1031"},"modified":"2016-02-16T15:22:43","modified_gmt":"2016-02-16T15:22:43","slug":"higher-python-reading-from-a-file","status":"publish","type":"post","link":"https:\/\/blogs.glowscotland.org.uk\/nl\/ColtnessHS-ComputingScience\/2016\/02\/16\/higher-python-reading-from-a-file\/","title":{"rendered":"Higher – Python – Reading from a file"},"content":{"rendered":"

\"Python-logo-notext.svg\"<\/a>A lot of people find reading from a sequential file<\/a> difficult. Well lets break it down, first of all what is a sequential file? A sequential file is a text based (ASCII or UNICODE) file that is made up of both printing and non printing characters. The end of the file is signalled with EoF<\/a>, often programmers put data in separate lines using a\u00a0new line\u00a0character<\/a>. Sometimes the files are in CSV format<\/a>, which means that each line holds a records worth of data.<\/p>\n

The basic premise of any Python read file access is<\/p>\n

    \n
  1. Open file for reading<\/li>\n
  2. read each line<\/li>\n
  3. close file<\/li>\n<\/ol>\n

    This post will mostly be focused on different ways of doing step 2.<\/p>\n

    <\/p>\n

    Getting a single piece of data from a file.<\/h2>\n

    <\/p>\n

    \n
    # Get single piece of data from a file and store in variable<\/span>\r\n\r\ntext_file =<\/span> open<\/span>('single_name.txt'<\/span>,'r'<\/span>) # 1. open file<\/span>\r\nname =<\/span> text_file.<\/span>read()                 # 2. read data from file<\/span>\r\ntext_file.<\/span>close()                       # 3. close file<\/span>\r\n\r\nprint<\/span>('The data in the file \"single_name.txt\" is'<\/span>,name)\r\n<\/pre>\n<\/div>\n
    Get multiple lines of data from\u00a0a file.<\/h2>\n
    <\/p>\n
    \n
    # Get multiple lines of data from a file and store in an array<\/span>\r\n# Unknown number of lines<\/span>\r\n\r\nnames=<\/span>[]\r\ntext_file =<\/span> open<\/span>('classList.txt'<\/span>,'r'<\/span>)   # 1. open file<\/span>\r\nfor<\/span> line in<\/span> text_file:                  # 2. read data from file<\/span>\r\n    names.<\/span>append(line[:-<\/span>1<\/span>])             #    The [:-1] removes the new line char<\/span>\r\ntext_file.<\/span>close()                       # 3. close file<\/span>\r\n\r\nprint<\/span>('The data in the file \"classList.txt\" is'<\/span>,names)\r\n<\/pre>\n<\/div>\n
    Reading from a CSV into records<\/h2>\n
    <\/p>\n
    \n\n\n\n
    \n
     1\r\n 2\r\n 3\r\n 4\r\n 5\r\n 6\r\n 7\r\n 8\r\n 9\r\n10\r\n11\r\n12<\/pre>\n<\/td>\n
    		\n
    # Get data from a CSV file, unknown number of lines<\/span>\r\n# Read into record<\/span>\r\n\r\nnames=<\/span>[]\r\n\r\ncsv_file =<\/span> open<\/span>('highscores.csv'<\/span>,'r'<\/span>)   # 1. Open file<\/span>\r\nfor<\/span> line in<\/span> csv_file:                   # 2. read data from file<\/span>\r\n    names.<\/span>append(line[:-<\/span>1<\/span>].<\/span>split(','<\/span>))  # split into two variables after removing newline         <\/span>\r\ncsv_file.<\/span>close()                        # 3. close file<\/span>\r\n\r\nprint<\/span>('High Scores'<\/span>)\r\nprint<\/span>(names)\r\n<\/pre>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n
    Read data from CSV file into arrays<\/h2>\n
    <\/p>\n
    \n\n\n\n
    \n
     1\r\n 2\r\n 3\r\n 4\r\n 5\r\n 6\r\n 7\r\n 8\r\n 9\r\n10\r\n11\r\n12\r\n13\r\n14\r\n15<\/pre>\n<\/td>\n
    		\n
    # Get data from a CSV file, unknown number of lines<\/span>\r\n# Read into seperate arrays<\/span>\r\n\r\nnames=<\/span>[]\r\nscores=<\/span>[]\r\ncsv_file =<\/span> open<\/span>('highscores.csv'<\/span>,'r'<\/span>)   # 1. Open file<\/span>\r\nfor<\/span> line in<\/span> csv_file:                   # 2. read data from file<\/span>\r\n    name,score=<\/span>line[:-<\/span>1<\/span>].<\/span>split(','<\/span>)     # split into two variables after removing newline<\/span>\r\n    names.<\/span>append(name)\r\n    scores.<\/span>append(int<\/span>(score))           # change score to Integer<\/span>\r\ncsv_file.<\/span>close()                        # 3. close file<\/span>\r\n\r\nprint<\/span>('High Scores'<\/span>)\r\nprint<\/span>(names)\r\nprint<\/span>(scores)\r\n<\/pre>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n
    There are other\u00a0constructs we can use to read data from files but the steps remain the same.<\/p>\n
      \n
    1. Open file for reading<\/li>\n
    2. read each line<\/li>\n
    3. close file<\/li>\n<\/ol>\n
      I have attached the files I used<\/p>\n