PY0101EN-4-1-ReadFile.ipynb

{"cells":[{"cell_type":"markdown","metadata":{},"source":["<center>\n","    <img src=\"https://cf-courses-data.s3.us.cloud-object-storage.appdomain.cloud/IBMDeveloperSkillsNetwork-PY0101EN-SkillsNetwork/IDSNlogo.png\" width=\"300\" alt=\"cognitiveclass.ai logo\"  />\n","</center>\n","\n","# Reading Files Python\n","\n","Estimated time needed: **40** minutes\n","\n","## Objectives\n","\n","After completing this lab you will be able to:\n","\n","*   Read text files using Python libraries\n"]},{"cell_type":"markdown","metadata":{},"source":["<h2>Table of Contents</h2>\n","<div class=\"alert alert-block alert-info\" style=\"margin-top: 20px\">\n","    <ul>\n","        <li><a href=\"https://download/?utm_medium=Exinfluencer&utm_source=Exinfluencer&utm_content=000026UJ&utm_term=10006555&utm_id=NA-SkillsNetwork-Channel-SkillsNetworkCoursesIBMDeveloperSkillsNetworkPY0101ENSkillsNetwork19487395-2021-01-01\">Download Data</a></li>\n","        <li><a href=\"https://read/?utm_medium=Exinfluencer&utm_source=Exinfluencer&utm_content=000026UJ&utm_term=10006555&utm_id=NA-SkillsNetwork-Channel-SkillsNetworkCoursesIBMDeveloperSkillsNetworkPY0101ENSkillsNetwork19487395-2021-01-01\">Reading Text Files</a></li>\n","        <li><a href=\"https://better/?utm_medium=Exinfluencer&utm_source=Exinfluencer&utm_content=000026UJ&utm_term=10006555&utm_id=NA-SkillsNetwork-Channel-SkillsNetworkCoursesIBMDeveloperSkillsNetworkPY0101ENSkillsNetwork19487395-2021-01-01\">A Better Way to Open a File</a></li>\n","    </ul>\n","\n","</div>\n","\n","<hr>\n"]},{"cell_type":"markdown","metadata":{},"source":["<h2 id=\"download\">Download Data</h2>\n"]},{"cell_type":"code","execution_count":null,"metadata":{},"outputs":[],"source":["import urllib.request\n","url = 'https://cf-courses-data.s3.us.cloud-object-storage.appdomain.cloud/IBMDeveloperSkillsNetwork-PY0101EN-SkillsNetwork/labs/Module%204/data/example1.txt'\n","filename = 'Example1.txt'\n","urllib.request.urlretrieve(url, filename)"]},{"cell_type":"code","execution_count":null,"metadata":{},"outputs":[],"source":["# Download Example file\n","\n","\n","!wget -O /resources/data/Example1.txt https://cf-courses-data.s3.us.cloud-object-storage.appdomain.cloud/IBMDeveloperSkillsNetwork-PY0101EN-SkillsNetwork/labs/Module%204/data/example1.txt"]},{"cell_type":"markdown","metadata":{},"source":["<hr>\n"]},{"cell_type":"markdown","metadata":{},"source":["<h2 id=\"read\">Reading Text Files</h2>\n"]},{"cell_type":"markdown","metadata":{},"source":["One way to read or write a file in Python is to use the built-in <code>open</code> function. The <code>open</code> function provides a **File object** that contains the methods and attributes you need in order to read, save, and manipulate the file. In this notebook, we will only cover **.txt** files. The first parameter you need is the file path and the file name. An example is shown as follow:\n"]},{"cell_type":"markdown","metadata":{},"source":["<img src=\"https://cf-courses-data.s3.us.cloud-object-storage.appdomain.cloud/IBMDeveloperSkillsNetwork-PY0101EN-SkillsNetwork/labs/Module%204/images/ReadOpen.png\" width=\"500\" />\n"]},{"cell_type":"markdown","metadata":{},"source":["The mode argument is optional and the default value is **r**. In this notebook we only cover two modes:\n","\n","<ul>\n","    <li>**r**: Read mode for reading files </li>\n","    <li>**w**: Write mode for writing files</li>\n","</ul>\n"]},{"cell_type":"markdown","metadata":{},"source":["For the next example, we will use the text file **Example1.txt**. The file is shown as follows:\n"]},{"cell_type":"markdown","metadata":{},"source":["<img src=\"https://cf-courses-data.s3.us.cloud-object-storage.appdomain.cloud/IBMDeveloperSkillsNetwork-PY0101EN-SkillsNetwork/labs/Module%204/images/ReadFile.png\" width=\"100\" />\n"]},{"cell_type":"markdown","metadata":{},"source":["We read the file:\n"]},{"cell_type":"code","execution_count":null,"metadata":{},"outputs":[],"source":["# Read the Example1.txt\n","\n","example1 = \"Example1.txt\"\n","file1 = open(example1, \"r\")"]},{"cell_type":"markdown","metadata":{},"source":["We can view the attributes of the file.\n"]},{"cell_type":"markdown","metadata":{},"source":["The name of the file:\n"]},{"cell_type":"code","execution_count":null,"metadata":{},"outputs":[],"source":["# Print the path of file\n","\n","file1.name"]},{"cell_type":"markdown","metadata":{},"source":["The mode the file object is in:\n"]},{"cell_type":"code","execution_count":null,"metadata":{},"outputs":[],"source":["# Print the mode of file, either 'r' or 'w'\n","\n","file1.mode"]},{"cell_type":"markdown","metadata":{},"source":["We can read the file and assign it to a variable :\n"]},{"cell_type":"code","execution_count":null,"metadata":{},"outputs":[],"source":["# Read the file\n","\n","FileContent = file1.read()\n","FileContent"]},{"cell_type":"markdown","metadata":{},"source":["The **/n** means that there is a new line.\n"]},{"cell_type":"markdown","metadata":{},"source":["We can print the file:\n"]},{"cell_type":"code","execution_count":null,"metadata":{},"outputs":[],"source":["# Print the file with '\\n' as a new line\n","\n","print(FileContent)"]},{"cell_type":"markdown","metadata":{},"source":["The file is of type string:\n"]},{"cell_type":"code","execution_count":null,"metadata":{},"outputs":[],"source":["# Type of file content\n","\n","type(FileContent)"]},{"cell_type":"markdown","metadata":{},"source":["It is very important that the file is closed in the end. This frees up resources and ensures consistency across different python versions.\n"]},{"cell_type":"code","execution_count":null,"metadata":{},"outputs":[],"source":["# Close file after finish\n","\n","file1.close()"]},{"cell_type":"markdown","metadata":{},"source":["<hr>\n"]},{"cell_type":"markdown","metadata":{},"source":["<h2 id=\"better\">A Better Way to Open a File</h2>\n"]},{"cell_type":"markdown","metadata":{},"source":["Using the <code>with</code> statement is better practice, it automatically closes the file even if the code encounters an exception. The code will run everything in the indent block then close the file object.\n"]},{"cell_type":"code","execution_count":null,"metadata":{},"outputs":[],"source":["# Open file using with\n","\n","with open(example1, \"r\") as file1:\n","    FileContent = file1.read()\n","    print(FileContent)"]},{"cell_type":"markdown","metadata":{},"source":["The file object is closed, you can verify it by running the following cell:\n"]},{"cell_type":"code","execution_count":null,"metadata":{},"outputs":[],"source":["# Verify if the file is closed\n","\n","file1.closed"]},{"cell_type":"markdown","metadata":{},"source":["We can see the info in the file:\n"]},{"cell_type":"code","execution_count":null,"metadata":{},"outputs":[],"source":["# See the content of file\n","\n","print(FileContent)"]},{"cell_type":"markdown","metadata":{},"source":["The syntax is a little confusing as the file object is after the <code>as</code> statement. We also don’t explicitly close the file. Therefore we summarize the steps in a figure:\n"]},{"cell_type":"markdown","metadata":{},"source":["<img src=\"https://cf-courses-data.s3.us.cloud-object-storage.appdomain.cloud/IBMDeveloperSkillsNetwork-PY0101EN-SkillsNetwork/labs/Module%204/images/ReadWith.png\" width=\"500\" />\n"]},{"cell_type":"markdown","metadata":{},"source":["We don’t have to read the entire file, for example, we can read the first 4 characters by entering three as a parameter to the method **.read()**:\n"]},{"cell_type":"code","execution_count":null,"metadata":{},"outputs":[],"source":["# Read first four characters\n","\n","with open(example1, \"r\") as file1:\n","    print(file1.read(4))"]},{"cell_type":"markdown","metadata":{},"source":["Once the method <code>.read(4)</code> is called the first 4 characters are called. If we call the method again, the next 4 characters are called. The output for the following cell will demonstrate the process for different inputs to the method <code>read()</code>:\n"]},{"cell_type":"code","execution_count":null,"metadata":{},"outputs":[],"source":["# Read certain amount of characters\n","\n","with open(example1, \"r\") as file1:\n","    print(file1.read(4))\n","    print(file1.read(4))\n","    print(file1.read(7))\n","    print(file1.read(15))"]},{"cell_type":"markdown","metadata":{},"source":["The process is illustrated in the below figure, and each color represents the part of the file read after the method <code>read()</code> is called:\n"]},{"cell_type":"markdown","metadata":{},"source":["<img src=\"https://cf-courses-data.s3.us.cloud-object-storage.appdomain.cloud/IBMDeveloperSkillsNetwork-PY0101EN-SkillsNetwork/labs/Module%204/images/read.png\" width=\"500\" />\n"]},{"cell_type":"markdown","metadata":{},"source":["Here is an example using the same file, but instead we read 16, 5, and then 9 characters at a time:\n"]},{"cell_type":"code","execution_count":null,"metadata":{},"outputs":[],"source":["# Read certain amount of characters\n","\n","with open(example1, \"r\") as file1:\n","    print(file1.read(16))\n","    print(file1.read(5))\n","    print(file1.read(9))"]},{"cell_type":"markdown","metadata":{},"source":["We can also read one line of the file at a time using the method <code>readline()</code>:\n"]},{"cell_type":"code","execution_count":null,"metadata":{},"outputs":[],"source":["# Read one line\n","\n","with open(example1, \"r\") as file1:\n","    print(\"first line: \" + file1.readline())"]},{"cell_type":"markdown","metadata":{},"source":["We can also pass an argument to <code> readline() </code> to specify the number of charecters we want to read. However, unlike <code> read()</code>, <code> readline()</code> can only read one line at most.\n"]},{"cell_type":"code","execution_count":null,"metadata":{},"outputs":[],"source":["with open(example1, \"r\") as file1:\n","    print(file1.readline(20)) # does not read past the end of line\n","    print(file1.read(20)) # Returns the next 20 chars\n"]},{"cell_type":"markdown","metadata":{},"source":["We can use a loop to iterate through each line:\n"]},{"cell_type":"code","execution_count":null,"metadata":{},"outputs":[],"source":["# Iterate through the lines\n","\n","with open(example1,\"r\") as file1:\n","        i = 0;\n","        for line in file1:\n","            print(\"Iteration\", str(i), \": \", line)\n","            i = i + 1"]},{"cell_type":"markdown","metadata":{},"source":["We can use the method <code>readlines()</code> to save the text file to a list:\n"]},{"cell_type":"code","execution_count":null,"metadata":{},"outputs":[],"source":["# Read all lines and save as a list\n","\n","with open(example1, \"r\") as file1:\n","    FileasList = file1.readlines()"]},{"cell_type":"markdown","metadata":{},"source":["Each element of the list corresponds to a line of text:\n"]},{"cell_type":"code","execution_count":null,"metadata":{},"outputs":[],"source":["# Print the first line\n","\n","FileasList[0]"]},{"cell_type":"markdown","metadata":{},"source":["# Print the second line\n","\n","FileasList\\[1]\n"]},{"cell_type":"code","execution_count":null,"metadata":{},"outputs":[],"source":["# Print the third line\n","\n","FileasList[2]"]},{"cell_type":"markdown","metadata":{},"source":["<hr>\n","<h2>The last exercise!</h2>\n","<p>Congratulations, you have completed your first lesson and hands-on lab in Python.\n","<hr>\n"]},{"cell_type":"markdown","metadata":{},"source":["## Author\n","\n","<a href=\"https://www.linkedin.com/in/joseph-s-50398b136/?utm_medium=Exinfluencer&utm_source=Exinfluencer&utm_content=000026UJ&utm_term=10006555&utm_id=NA-SkillsNetwork-Channel-SkillsNetworkCoursesIBMDeveloperSkillsNetworkPY0101ENSkillsNetwork19487395-2021-01-01\" target=\"_blank\">Joseph Santarcangelo</a>\n","\n","## Other contributors\n","\n","<a href=\"https://www.linkedin.com/in/jiahui-mavis-zhou-a4537814a?utm_medium=Exinfluencer&utm_source=Exinfluencer&utm_content=000026UJ&utm_term=10006555&utm_id=NA-SkillsNetwork-Channel-SkillsNetworkCoursesIBMDeveloperSkillsNetworkPY0101ENSkillsNetwork19487395-2021-01-01\">Mavis Zhou</a>\n","\n","## Change Log\n","\n","| Date (YYYY-MM-DD) | Version | Changed By    | Change Description                                        |\n","| ----------------- | ------- | ------------- | --------------------------------------------------------- |\n","| 2022-01-10        | 2.1     | Malika        | Removed the readme for GitShare                           |\n","| 2020-09-30        | 1.3     | Malika        | Deleted exericse \"Weather Data\"                           |\n","| 2020-09-30        | 1.2     | Malika Singla | Weather Data dataset link added                           |\n","| 2020-09-30        | 1.1     | Arjun Swani   | Added exericse \"Weather Data\"                             |\n","| 2020-09-30        | 1.0     | Arjun Swani   | Added blurbs about closing files and read() vs readline() |\n","| 2020-08-26        | 0.2     | Lavanya       | Moved lab to course repo in GitLab                        |\n","|                   |         |               |                                                           |\n","|                   |         |               |                                                           |\n","\n","<hr/>\n","\n","## <h3 align=\"center\"> © IBM Corporation 2020. All rights reserved. <h3/>\n"]}],"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":"3.7.6"}},"nbformat":4,"nbformat_minor":4}