This lesson is being piloted (Beta version)

Python for Dynamics and Evolution of Earth and Planets: Glossary

Key Points

Analyzing Tabular Data
  • Import a library into a program using import libraryname.

  • Use the numpy library to work with arrays in Python.

  • Use variable = value to assign a value to a variable in order to record it in memory.

  • Variables are created on demand whenever a value is assigned to them.

  • Use print(something) to display the value of something.

  • The expression array.shape gives the shape of an array.

  • Use array[x, y] to select a single element from a 2D array.

  • Array indices start at 0, not 1.

  • Use low:high to specify a slice that includes the indices from low to high-1.

  • All the indexing and slicing that works on arrays also works on strings.

  • Use # some kind of explanation to add comments to programs.

  • Use numpy.mean(array), numpy.max(array), and numpy.min(array) to calculate simple statistics.

  • Use numpy.mean(array, axis=0) or numpy.mean(array, axis=1) to calculate statistics across the specified axis.

  • Use the pyplot library from matplotlib for creating simple visualizations.

Repeating Actions with Loops
  • Use for variable in sequence to process the elements of a sequence one at a time.

  • The body of a for loop must be indented.

  • Use len(thing) to determine the length of something that contains other values.

Storing Multiple Values in Lists
  • [value1, value2, value3, ...] creates a list.

  • Lists can contain any Python object, including lists (i.e., list of lists).

  • Lists are indexed and sliced with square brackets (e.g., list[0] and list[2:9]), in the same way as strings and arrays.

  • Lists are mutable (i.e., their values can be changed in place).

  • Strings are immutable (i.e., the characters in them cannot be changed).

Analyzing Data from Multiple Files
  • Use glob.glob(pattern) to create a list of files whose names match a pattern.

  • Use * in a pattern to match zero or more characters, and ? to match any single character.

Making Choices
  • Use if condition to start a conditional statement, elif condition to provide additional tests, and else to provide a default.

  • The bodies of the branches of conditional statements must be indented.

  • Use == to test for equality.

  • X and Y is only true if both X and Y are true.

  • X or Y is true if either X or Y, or both, are true.

  • Zero, the empty string, and the empty list are considered false; all other numbers, strings, and lists are considered true.

  • True and False represent truth values.

Working with Pandas dataframes
Working with xarray
Making plots with python
Creating Functions
  • Define a function using def function_name(parameter).

  • The body of a function must be indented.

  • Call a function using function_name(value).

  • Numbers are stored as integers or floating-point numbers.

  • Variables defined within a function can only be seen and used within the body of the function.

  • If a variable is not defined within the function it is used, Python looks for a definition before the function call

  • Use help(thing) to view help for something.

  • Put docstrings in functions to provide help for that function.

  • Specify default values for parameters when defining a function using name=value in the parameter list.

  • Parameters can be passed by matching based on name, by position, or by omitting them (in which case the default value is used).

  • Put code whose parameters change frequently in a function, then call it with different parameter values to customize its behavior.

Errors and Exceptions
  • Tracebacks can look intimidating, but they give us a lot of useful information about what went wrong in our program, including where the error occurred and what type of error it was.

  • An error having to do with the ‘grammar’ or syntax of the program is called a SyntaxError. If the issue has to do with how the code is indented, then it will be called an IndentationError.

  • A NameError will occur if you use a variable that has not been defined, either because you meant to use quotes around a string, you forgot to define the variable, or you just made a typo.

  • Containers like lists and strings will generate errors if you try to access items in them that do not exist. This type of error is called an IndexError.

  • Trying to read a file that does not exist will give you an FileNotFoundError. Trying to read a file that is open for writing, or writing to a file that is open for reading, will give you an IOError.

Command-Line Programs
  • The sys library connects a Python program to the system it is running on.

  • The list sys.argv contains the command-line arguments that a program was run with.

  • Avoid silent failures.

  • The pseudo-file sys.stdin connects to a program’s standard input.

  • The pseudo-file sys.stdout connects to a program’s standard output.

Defensive Programming
  • Program defensively, i.e., assume that errors are going to arise, and write code to detect them when they do.

  • Put assertions in programs to check their state as they run, and to help readers understand how those programs are supposed to work.

  • Use preconditions to check that the inputs to a function are safe to use.

  • Use postconditions to check that the output from a function is safe to use.

  • Write tests before writing code in order to help determine exactly what that code is supposed to do.

  • Know what code is supposed to do before trying to debug it.

  • Make it fail every time.

  • Make it fail fast.

  • Change one thing at a time, and for a reason.

  • Keep track of what you’ve done.

  • Be humble.

Data analysis with Python
Visualize and publish with Python
Object Oriented Programming with Python
Automated testing
  • collaborative testing/code review workflow

  • pytest

  • travis

Organize and distribute a Python package
  • software license

  • pypi

  • conda

  • Software documentation

  • DevOps and automation

Parallelize your code
Check and improve the performance of your code