Getting Started
- Use the Spyder IDE for editing and running Python
- The IPython console can be used to interact with Python directly
- The editor can be used to write code, run and save it
Variables and Assignment
- Use variables to store values.
- Use
print
to display values. - Variables persist between cells.
- Variables must be created before they are used.
- Variables can be used in calculations.
- Use an index to get a single character from a string.
- Use a slice to get a substring.
- Use the built-in function
len
to find the length of a string. - Python is case-sensitive.
- Use meaningful variable names.
Data Types and Type Conversion
- Every value has a type.
- Use the built-in function
type
to find the type of a value. - Types control what operations can be done on values.
- Strings can be added and multiplied.
- Strings have a length (but numbers don’t).
- Must convert numbers to strings or vice versa when operating on them.
- Can mix integers and floats freely in operations.
- Variables only change value when something is assigned to them.
Built-in Functions and Help
- Use comments to add documentation to programs.
- A function may take zero or more arguments.
- Commonly-used built-in functions include
max
,min
, andround
. - Functions may only work for certain (combinations of) arguments.
- Functions may have default values for some arguments.
- Use the built-in function
help
to get help for a function. - Every function returns something.
- Python reports a syntax error when it can’t understand the source of a program.
- Python reports a runtime error when something goes wrong while a program is executing.
- Fix syntax errors by reading the source code, and runtime errors by tracing the program’s execution.
Morning Coffee
Libraries
- Most of the power of a programming language is in its libraries.
- A program must import a library module in order to use it.
- Use
help
to learn about the contents of a library module. - Import specific items from a library to shorten programs.
- Create an alias for a library when importing it to shorten programs.
Lunch
Lists
- A list stores many values in a single structure.
- Use an item’s index to fetch it from a list.
- Lists’ values can be replaced by assigning to them.
- Appending items to a list lengthens it.
- Use
del
to remove items from a list entirely. - The empty list contains no values.
- Lists may contain values of different types.
- Character strings can be indexed like lists.
- Character strings are immutable.
- Indexing beyond the end of the collection is an error.
For Loops
- A for loop executes commands once for each value in a collection.
- The first line of the
for
loop must end with a colon, and the body must be indented. - Indentation is always meaningful in Python.
- A
for
loop is made up of a collection, a loop variable, and a body. - Loop variables can be called anything (but it is strongly advised to have a meaningful name to the looping variable).
- The body of a loop can contain many statements.
- Use
range
to iterate over a sequence of numbers. - The Accumulator pattern turns many values into one.
Looping Over Data Sets
- Use a
for
loop to process files given a list of their names. - Use
glob.glob
to find sets of files whose names match a pattern. - Use
glob
andfor
to process batches of files.
Writing Functions
- Break programs down into functions to make them easier to understand.
- Define a function using
def
with a name, parameters, and a block of code. - Defining a function does not run it.
- Arguments in call are matched to parameters in definition.
- Functions may return a result to their caller using
return
.
Variable Scope
- The scope of a variable is the part of a program that can ‘see’ that variable.
Afternoon Coffee
Conditionals
- Use
if
statements to control whether or not a block of code is executed. - Conditionals are often used inside loops.
- Use
else
to execute a block of code when anif
condition is not true. - Use
elif
to specify additional tests. - Conditions are tested once, in order.
- Create a table showing variables’ values to trace a program’s execution.
Programming Style
- Follow standard Python style in your code.
- Use docstrings to provide online help.
Wrap-Up
- Python supports a large community within and outwith research.
Feedback
- We are constantly seeking to improve this course.