An Introduction to Programming for Bioscientists: A Python-Based Primer
Fig 1
Strings in Python: anatomy and basic behavior.
The anatomy and basic behavior of Python strings are shown, as samples of actual code (left panel) and corresponding conceptual diagrams (right panel). The Python interpreter prompts for user input on lines beginning with >>> (leftmost edge), while a starting … denotes a continuation of the previous line; output lines are not prefixed by an initial character (e.g., the fourth line in this example). Strings are simply character array objects (of type str), and a sample string-specific method (replace) is shown on line 3. As with ordinary lists, strings can be ‘sliced’ using the syntax shown here: the first list element to be included in the slice is indexed by start, and the last included element is at stop-1, with an optional stride of size step (defaults to one). Concatenation, via the + operator, is the joining of whole strings or subsets of strings that are generated via slicing (as in this case). For clarity, the integer indices of the string positions are shown only in the forward (left to right) direction for mySnake1 and in the reverse direction for mySnake2. These two strings are sliced and concatenated to yield the object newSnake; note that slicing mySnake1 as [0:7] and not [0:6] means that a whitespace char is included between the two words in the resultant newSnake, thus obviating the need for further manipulations to insert whitespace (e.g., concatenations of the form word1+' '+word2).