User-defined Functions:gcufbioinfo

Here is the process for creating your own function in Python. The first line begins with the keyword def, is followed by the name of the function and any arguments (expected input values) surrounded by parentheses, and ends with a colon. Subsequent lines make up the body of the function and must be indented. If a string comment appears in the first line of the body, it becomes part of the documentation for the function. The last line of a function returns a result.
Let's define some functions in the PyCrust shell. Then we can try each function with some sample data and see the result returned by the function.

>>> def transcribe(dna): 
...     """Return dna string as rna string.""" 
...     return dna.replace('T', 'U') 
...      
>>> transcribe('CCGGAAGAGCTTACTTAG') 
'CCGGAAGAGCUUACUUAG' 

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Python Lists:gcufbioinfo

Where Python strings are limited to characters, Python lists have no limitations. Python lists are ordered sequences of arbitrary Python objects, including other lists. In addition, you can insert, delete and replace elements in a list. Lists are written as a series of objects, separated by commas, inside of square brackets. Let's look at some lists, and some operations you can perform on lists.

>>> bases = ['A', 'C', 'G', 'T'] 
>>> bases 
['A', 'C', 'G', 'T'] 
>>> bases.append('U') 
>>> bases 
['A', 'C', 'G', 'T', 'U'] 
>>> bases.reverse() 
>>> bases 
['U', 'T', 'G', 'C', 'A'] 
>>> bases[0] 
'U' 
>>> bases[1] 
'T' 
>>> bases.remove('U') 
>>> bases 
['T', 'G', 'C', 'A'] 
>>> bases.sort() 
>>> bases 
['A', 'C', 'G', 'T']

In this example we created a list of single characters that we called bases.
Then we added an element to the end, reversed the order of all the elements,
retrieved elements by their index position, removed an element with the value
'U', and sorted the elements. Removing an element from a list
illustrates a situation where we need to supply the remove()
method with an additional piece of information, namely the value that we want
to remove from the list. As you can see in the picture below, PyCrust takes
advantage of Python's ability to let us know what is required for most

operations by displaying that information in a call tip pop-up window.  

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