A few examples:
>>> print abs(-10) # The function is 'abs'. Its argument is -10. 10 >>> # The functions are 'min' and 'max'. They take an # arbitrary number of arguments. >>> max(3,6,8,2) 8 >>> min(3,6,8,2) 2 >>> # 'sum' takes 1 or two arguments >>> sum([5, 10, 15]) 30 >>> sum([5, 10, 15], 10) 40 >>>The list of Python's built-in functions are listed in the Python documentation. Many more functions are available in the modules.
You can make your own functions or redefine the built-in ones using the def statement. This is described in more detail in a later lecture.
>>> seq = "AATGCCG"
>>> seq.lower()
'aatgccg'
>>> seq.count("A")
2
>>> seq.find("GC")
3
>>> seq.find("gc")
-1
>>> seq.replace("C", "U")
'AATGUUG'
>>> import string
>>> seq.translate(string.maketrans("ATCG", "TAGC"))
'TTACGGC'
>>> # Make the reverse complement
>>> seq.translate(string.maketrans("ATCG", "TAGC"))[::-1]
'CGGCATT'
>>> "This is some words separated by spaces.".split()
['This', 'is', 'some', 'words', 'separated', 'by', 'spaces.']
>>> "This is some words separated by spaces.".split("s")
['Thi', ' i', ' ', 'ome word', ' ', 'eparated by ', 'pace', '.']
>>>
Some methods are used so often they have special syntax.
>>> s = "AATGCCGTTTAT" >>> s[0] # index 'A' >>> s[1:4] # slice from beginning to end 'ATG' >>> s[:4] # default beginning is position 0 'AATG' >>> s[-1] # index from the end 'T' >>> s[-3:] # default end includes the last character 'TAT' >>> s[3:-3] 'GCCGTT' >>> s[::2] # the optional third parameter is the stride 'ATCGTA' >>> s[::-1] # returns the string, reversed 'TATTTGCCGTAA' >>>
Here's a simple way to swap the value of two variables in one step:
onions, potatoes = potatoes, onions
NOTE: The obvious alternative DOES NOT work:
onion = potatoes potatoes = onions # oops!
Here is a correct non-idiomatic alternative
tmp = onions onions = potatoes potatoes = tmp
onions, potatoes, turnips = potatoes, turnips, onions
This page based on
Functions.
*Taken from Learning Python.