3: Standard Library Functions
- Page ID
- 431395
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)There are many modules that do not load into memory when you start Python, but they come with the installation, and these contain functions that you can use, but you must import them to use them. It is best practice to put all of your import statements at the top of your code, so someone who is reading it can instantly see what modules you need to import. These modules are single files that can define functions, classes and variables. To use a function you treat it as a class method, with the following syntax
module_name.function_name(arguments)
To find what type of modules you have installed you can run the following command on your computer or Raspberry Pi
#the following code will list the modules installed on your computer. help('modules')
If you want to see what modules are running on the Jupyter Hub of LibreText you can run the command below. It will take a minute, and probably give you a few warnings.
To run a module you first need to import it
Import Statement
The import statement loads a module into the program's memory. Please go to the modules section to learn about specific modules. To see this, we will look at the random module. The following code will generate an integer between 1 and 999.
The above failed because we did not load the random module into memory
Note, if you ran the code above, you loaded the random module into memory, and you do not need to reload it (the code that did not work will now work).
Checking the class of the random module
Some Common Standard Modules
Here are some of the standard modules we will use in this class. Any code that uses these functions must first import them.
random
Random Seed
Random seed lets you reproduce a random number every time.
re Regular Expressions
Socket
The socket module lets you work with network protocols and enable communication between devices over the network. we use it in the "Find IP Address" code that we use to get the IP address of the Raspberry Pi
Subprocess
- Docs Page
- This allows you to start other processes from your python code, and these can be run in different languages. For example, the following code on a windows machine will read the current directory from the command line. NOTE: if you are on a WINDOWS machine, change the "ls" to "dir", as that is the windows command for showing files in the current directory.
import subprocess result = subprocess.run(["ls"], shell=True, capture_output=True, text=True) print(result.stdout)
So the above code runs the BASH command ls from python
time
- Docs Page
- provides functions to work with time related tasks
- epoch time is the number of seconds since Jan 1, 1970
- the sleep function is very useful in data collection, but you must be careful if you run it before or after a process, as in the later case, the process time is added to the sleep time.
urllib