Len
The len() function will return the length of a string or the number of items in a list. >>> spam = ['cat', 'dog', 'moose'] >>> len(spam) 3 >>> len('European Swallow') 16
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List
A list is just like it sounds. A list of things in sequence. A list value is a list. A list can be stored in a variable or passed to a function . Example list: ['cat', 'bat', 'rat', 'elephant'] Values inside the list are called items Items are comma-delimited This is an empty list: []
List Concatenation And Replication
Just like with strings lists can be concatenated and replicated with + and *. >>> [1, 2, 3] + ['A', 'B', 'C'] [1, 2, 3, 'A', 'B', 'C'] >>> ['X', 'Y', 'Z'] * 3 ['X', 'Y', 'Z', 'X', 'Y', 'Z', 'X', 'Y', 'Z'] >>> spam = [1, 2, 3] >>> spam = spam + ['A', 'B', 'C']
Local And Global Scope
Local Scope # Variables that are assigned inside a function have a local scope to that function. These are called local variables. Global Scope # Variables that have a global scope are (typically) defined outside of functions. These are called global variables. Global Statements # Global variables can be modified in a function with a global statement . Why do scopes matter? # Code in global scope cannot use local variables Code in local scope can access global variables Code in a function’s local scope cannot use variables in any other local scope You can use the same name for different variables if they are in different scopes. ...
lower()
Converts string to lowercase. >>> spam = 'Hello, world!' >>> spam.lower() 'hello, world!'
Making Scripts Executable
chmod 755 scriptfile (Or 700 if only executable by owner) ls -l script_file # to check ./script_file # to execute the script
Math Operators
Math Operators from Highest to Lowest Precedence Operator Operation Example Evaluates to… ** Exponenent 2 ** 3 8 % Modulus/remainder 22 % 8 6 // Integer division/floored quotient 22 // 8 2 / Division 22 / 8 2.75 * Multiplication 3 * 5 15 - Subtraction 5 - 2 3 + Addition 2 + 2 4
Method
A Methods is like functions except that it’s called on a value. Example using index() function. >>> spam = ['hello', 'hi', 'howdy', 'heyas'] >>> spam.index('hello') 0 >>> spam.index('heyas') 3 Note the syntax is value.method(someDataType) Unlike functions methods don’t return a value . Methods belong to a single date type. For example: lists, strings, etc.
Multiline Strings
A multiline string begins and ends with either 3 single-quotes or double-quotes. print('''Dear Alice, Eve's cat has been arrested for catnapping, cat burglary, and extortion. Sincerely, Bob''') Note, escape characters aren’t necessary in multiline strings. Multiline Comments # A multiline string is often used for multiline comments. """This is a test Python program. Written by Al Sweigart [email protected] this program was designed for Python 3, not Python 2. """ def spam(): """This is a multiline comment to help explain what the spam() function does. ...
Multiple Assignment Trick
You can assign multiple values to list items with the multiple assignment trick also called tuple unpacking. This is a shortcut technique as opposed to assigning each variable individually. >>> cat = ['fat', 'gray', 'loud'] >>> size, color, disposition = cat >>> cat ['fat', 'gray', 'loud'] >>> size 'fat' >>> color 'gray' >>> disposition 'loud' >>>