>>> 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 # 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
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*Taken from Learning Python.