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moved Dict notebook after R/W Files notebook
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‎005_Write_Your_Own_Functions.ipynb‎

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"metadata": {},
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"source": [
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"<!--NAVIGATION-->\n",
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"[< Loops](004_Loops.ipynb) | [Contents](index.ipynb) | [Dictionaries and Metadata >](006_Dictionaries_and_Metadata.ipynb)"
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"[< Loops](004_Loops.ipynb) | [Contents](index.ipynb) | [Read and Write Text Files >](006_Read_and_Write_Text_Files.ipynb)"
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]
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}
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],

007_Read_and_Write_Text_Files.ipynb renamed to 006_Read_and_Write_Text_Files.ipynb

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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"Now that you understand about `list` and `dict` as well as how to write your own functions with loops and conditional statements, you can already write simply programs that perform quite useful operations. \n",
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"You have learned about lists as well as how to write your own functions with loops and conditional statements. As such, you can already write programs performing a variety of tasks. \n",
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"\n",
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"However, as a research assistant, you will likely need to access data that are (locally or remotely) stored in files. A file provides a mechanism for **permanently store** information so that they can be retrieved when your program and/or your machine are restarted.\n",
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"However, something that is currently missing is a mechanism to access the data that you want to analyze. A very common way to access these data is through (local or remotely-stored) [files](https://en.wikipedia.org/wiki/Computer_file)."
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"<img align=\"left\" width=\"6%\" style=\"padding-right:10px;\" src=\"images/key.png\">\n",
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"\n",
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"There are two main types of files:"
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"A **file** provides a mechanism for **permanently storing information** so that they can be retrieved when your program and/or your machine are restarted."
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"There are two main types of files: text files and binary files."
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]
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},
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{
@@ -57,7 +71,7 @@
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"source": [
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"<img align=\"left\" width=\"6%\" style=\"padding-right:10px;\" src=\"images/info.png\">\n",
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"\n",
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"A very simple test to evaluate whether a given file is or not a text file is to try opening it using a text editor. If you can understand the visualized content, then that is file is likely a text file. *(Be warned that opening a file in this way can take a long time depending on the size of the file.)*"
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"A very simple test to evaluate whether a given file is a text file is to open it in a text editor. If you can understand the visualized content of an opened file, then the file is likely a text file. *(Be warned that opening a file in this way can take a long time depending on the size of the file.)*"
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]
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},
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{
@@ -105,17 +119,25 @@
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"source": [
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"In particular, we will explore the `os.path` sub-module to retrieve some data files that are stored on the server's hard disk.\n",
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"\n",
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"The first required operation is to **import** the `os` module. Then, we will use some of the `os.path` sub-module functionalities and variables to write a function that returns the full path of the server's folder where this notebook is located:\n",
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"The first required operation is to **import** the `os` module. Then, we will use some of the `os.path` sub-module functionalities and variables to write a function that returns the full path of the folder where this notebook is located:\n",
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"\n",
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"- `curdir`: The constant string used by the operating system to refer to the current directory. E.g., `.` for Windows and Linux.\n",
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"- `abspath()`: A function that returns the full, absolute version of a path."
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"outputs": [],
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"execution_count": 1,
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"metadata": {},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"The current folder is: C:\\code\\hyo2\\epom\\python_basics\n"
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]
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}
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],
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"source": [
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"import os\n",
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"\n",
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"The data are inside a `data` sub-folder. We now extend the previous code using `os.path.join()` and `os.path.exist()` functions to:\n",
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"As show in the figure below, the data are inside a `data` sub-folder: \n",
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"\n",
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"![Function Terminology](images/007_100_data_folder.png)"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"As such, we extend the previous code using `os.path.join()` and `os.path.exist()` functions to:\n",
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"\n",
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"- Create the full path to the `data` sub-folder.\n",
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"- Check whether the resulting path actually exists."
@@ -140,14 +171,22 @@
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"In case that the `data` sub-folder does not exist, we raise an error using the `raise` keyword."
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"In case that the `data` sub-folder does not exist, we raise an error using the [`raise`](https://docs.python.org/3.6/tutorial/errors.html#raising-exceptions) keyword."
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"outputs": [],
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"execution_count": 2,
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"metadata": {},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"The data folder is: C:\\code\\hyo2\\epom\\python_basics\\data\n"
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]
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}
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],
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"source": [
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"def get_data_folder():\n",
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" cur_folder = os.path.abspath(os.path.curdir)\n",
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"We will now retrieve all the paths to the files in the `data` sub-folder. Specifically, we will create a function `get_data_paths()` that will returns a list containing all the files in that folder, using the `os.listdir()` function."
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"We will now retrieve all the paths to the files in the `data` sub-folder. Specifically, we will create a function `get_data_paths()` that returns a list containing all the files in that folder, using the `os.listdir()` function."
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"outputs": [],
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"execution_count": 3,
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"metadata": {},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"The data paths are: ['C:\\\\code\\\\hyo2\\\\epom\\\\python_basics\\\\data\\\\ctd.txt', 'C:\\\\code\\\\hyo2\\\\epom\\\\python_basics\\\\data\\\\sal.txt', 'C:\\\\code\\\\hyo2\\\\epom\\\\python_basics\\\\data\\\\temp.txt']\n"
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]
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}
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],
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"source": [
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"def get_data_paths():\n",
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" data_paths = list() # create a empty list that will be populate and returned\n",
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"source": [
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"In the above code, we wrote a function in which:\n",
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"\n",
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"- We created and populated a list: `data_paths`\n",
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"- We reused a function that we previously created: `get_data_folder()`.\n",
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"- We used several Python functions from the `os` module: e.g., `listdir()`, `join()`.\n",
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"- We executed a `for` loop to populate the `data_paths` list.\n",
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"- We returned the populated list."
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"- We create and populate a list: `data_paths`\n",
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"- We reuse a function that was previously created: `get_data_folder()`.\n",
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"- We use several Python functions from the `os` module: e.g., `listdir()`, `join()`.\n",
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"- We execute a `for` loop to populate the `data_paths` list.\n",
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"- We return the populated list."
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]
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},
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{
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"source": [
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"<img align=\"left\" width=\"6%\" style=\"padding-right:10px;\" src=\"images/key.png\">\n",
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"\n",
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"You don't need to remember all the names of the available Python functions. But you need to learn how to search for them. The [official Python documentation](https://docs.python.org/3.6/index.html) is usually a good place to start with."
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"You don't need to remember all the names of the available Python functions. But you need to learn how to search for them. The [official Python documentation](https://docs.python.org/3.6/index.html) is a good place to start with."
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"From the [Lists of Variables notebook](002_Lists_of_Variables.ipynb), you should remember how to access a value in a list by its index. \n",
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"From the [Lists of Variables notebook](002_Lists_of_Variables.ipynb), you know how to access a value in a list by its index. \n",
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"\n",
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"Thus, to access the file named `sal.txt`, we can use `1` as index since it is the **second** element in the list."
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"outputs": [],
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"execution_count": 4,
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"metadata": {},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"The file path with index 1 is: C:\\code\\hyo2\\epom\\python_basics\\data\\sal.txt\n"
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]
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}
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],
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"source": [
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"sal_path = retrieved_paths[1]\n",
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"print(\"The file path with index 1 is: \" + sal_path)"
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"In the next section, you will learn how to open and read the content of these text files."
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"In the next section, you will learn how to open and read the content of `sal_path`."
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]
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"The Python `open()` function takes the name of the file (as a parameter) and returns a file object. \n",
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"<img align=\"left\" width=\"6%\" style=\"padding-right:10px;\" src=\"images/key.png\">\n",
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"\n",
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"This object can be used to read the sequence of characters in a few ways:"
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"The Python `open()` function takes the name of the file (as a parameter) and returns a [file object](https://docs.python.org/3.6/glossary.html#term-file-object). "
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"This file object can be used to read the sequence of characters in a few ways:"
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]
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{
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"outputs": [],
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"execution_count": 5,
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"metadata": {},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"31.4\n",
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"31.6\n",
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"30.5\n",
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"30.8\n",
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"30.4\n",
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"31.4\n",
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"31.6\n",
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"30.5\n",
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"30.3\n",
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"30.2\n",
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"31.4\n",
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"31.6\n",
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"32.5\n",
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"30.8\n",
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"31.4\n",
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"31.7\n",
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"31.6\n",
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"31.5\n",
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"30.2\n",
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"30.4\n",
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"\n"
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]
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}
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],
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"source": [
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"sal_file = open(sal_path)\n",
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"\n",
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"The execution of the above code will print the 20 salinity values in the text file. Although they look like numbers, they are actually just a single `str` of 100 characters!"
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"The execution of the above code will print the 20 salinity values in the text file. Although they look like numbers, they are **actually** a single `str` of 100 characters!"
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]
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},
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{
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"source": [
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"<img align=\"left\" width=\"6%\" style=\"padding-right:10px;\" src=\"images/info.png\">\n",
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"\n",
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"Why the characters are 100? Each row has 4 visible characters (e.g., `30.8`) but there is also an invisible character that the text editor interprets as a new line. Thus, `(4+1) * 20 = 100` characters."
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"Why the characters are 100? Each row has 4 visible characters (e.g., `30.8`) but there is also an invisible character (i.e., `\\n`) that the text editor interprets as a new line. Thus, `(4+1) * 20 = 100` characters."
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"We will now write a function that reads the sequence of characters, but also split them by line (using the `str` method named `splitlines()`) and convert the result in the corresponding `float` value."
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"We will now write a function that not only reads the sequence of characters, but also splits them by line (using the `str` method named `splitlines()`) and converts the result in the corresponding `float` value."
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]
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{
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"source": [
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"<img align=\"left\" width=\"6%\" style=\"padding-right:10px;\" src=\"images/info.png\">\n",
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"\n",
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"There are more efficient ways to read a text file. We adopted an approach that is simple to understand for a first learner."
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"There are more efficient ways to read a text file. We adopted an approach that is simple to understand for a first-time learner."
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]
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"The first required decision is the location on where to store the text file. For this collection of notebook, we will use the `output` sub-folder that can be retrieved running the following code:"
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"If you want to write a text file, the first decision to take is the location on where to store the text file. For this collection of notebook, we will use the `output` sub-folder that can be retrieved running the following code:"
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {},
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"outputs": [],
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"execution_count": 6,
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"metadata": {},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"The output folder is: C:\\code\\hyo2\\epom\\python_basics\\output\n"
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]
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}
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],
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"source": [
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"def get_output_folder():\n",
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" cur_folder = os.path.abspath(os.path.curdir)\n",
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"We then use `join()` function to store the output file: e.g., `depths.txt`."
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"We then use the `join()` function to set the output file: e.g., `depths.txt`."
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"To write a file, you have to use the `open()` passing the mode `w` as second parameter. We put this function within a function that take a list as a second parameter and write the content into the text file."
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"To write a file, you have to use the `open()` function and pass the `w` mode (`w` is for *write*) as second parameter. We put this function within a function that take a list as a second parameter and write the content into the text file."
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{
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"cell_type": "code",
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"execution_count": 7,
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"metadata": {},
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"outputs": [],
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"source": [
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" * [The os module](https://docs.python.org/3.6/library/os.html)\n",
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" * [Input and Output](https://docs.python.org/3.6/tutorial/inputoutput.html)\n",
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"* [Cross-platform software](https://en.wikipedia.org/wiki/Cross-platform_software)\n",
639-
"* [Text file](https://en.wikipedia.org/wiki/Text_file)\n",
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"* [Binary file](https://en.wikipedia.org/wiki/Binary_file)\n",
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"* [Filename extension](https://en.wikipedia.org/wiki/Filename_extension)"
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"* [Computer file](https://en.wikipedia.org/wiki/Computer_file)\n",
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" * [Text file](https://en.wikipedia.org/wiki/Text_file)\n",
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" * [Binary file](https://en.wikipedia.org/wiki/Binary_file)\n",
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" * [Filename extension](https://en.wikipedia.org/wiki/Filename_extension)"
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]
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},
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{
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"metadata": {},
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"source": [
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"<!--NAVIGATION-->\n",
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"[< Dictionaries and Metadata](006_Dictionaries_and_Metadata.ipynb) | [Contents](index.ipynb) | [A Class as a Data Container>](008_A_Class_as_a_Data_Container.ipynb)"
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"[< Write Your Own Functions](005_Write_Your_Own_Functions.ipynb) | [Contents](index.ipynb) | [Dictionaries and Metadata >](007_Dictionaries_and_Metadata.ipynb)"
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]
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}
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],

006_Dictionaries_and_Metadata.ipynb renamed to 007_Dictionaries_and_Metadata.ipynb

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"metadata": {},
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"source": [
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"<!--NAVIGATION-->\n",
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"[< Write Your Own Functions](005_Write_Your_Own_Functions.ipynb) | [Contents](index.ipynb) | [Read and Write Text Files >](007_Read_and_Write_Text_Files.ipynb)"
693+
"[< Read and Write Text Files >](006_Read_and_Write_Text_Files.ipynb) | [Contents](index.ipynb) | [A Class as a Data Container >](008_A_Class_as_a_Data_Container.ipynb)"
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]
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}
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],

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