Programming with Python
Basic data types in Python include integers, strings, and
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
print(something) to display the value of
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Built-in functions are always available to use.
Import a library into a program using
numpy library to work with arrays in
array.shape gives the shape of an
array[x, y] to select a single element from a 2D
Array indices start at 0, not 1.
low:high to specify a
includes the indices from
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numpy.amin(array) to calculate simple statistics.
numpy.mean(array, axis=0) or
numpy.mean(array, axis=1) to calculate statistics across
the specified axis.
pyplot module from the
library for creating simple visualizations.
[value1, value2, value3, ...] creates a list.
Lists can contain any Python object, including lists (i.e., list of
Lists are indexed and sliced with square brackets (e.g.,
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
for variable in sequence to process the elements of
a sequence one at a time.
The body of a
for loop must be indented.
len(thing) to determine the length of something
that contains other values.
glob.glob(pattern) to create a list of files whose
names match a pattern.
* in a pattern to match zero or more characters,
? to match any single character.
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
== to test for equality.
X and Y is only true if both
Y are true.
X or Y is true if either
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.
False represent truth
Define a function using
The body of a function must be indented.
Call a function using
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.
Variables created outside of any function are called global
Within a function, we can access global variables.
Variables created within a function override global variables if
their names match.
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.
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
SyntaxError. If the issue has to do with how the
code is indented, then it will be called an
NameError will occur when trying to use a variable
that does not exist. Possible causes are that a variable definition is
missing, a variable reference differs from its definition in spelling or
capitalization, or the code contains a string that is missing quotes
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
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
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 postconditions to check that the output from a function is safe
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.
sys library connects a Python program to the system
it is running on.
sys.argv contains the command-line arguments
that a program was run with.
Avoid silent failures.
sys.stdin connects to a program’s