Python Tips

= Python tips :hp-tags: python, tips

==== What’s here ?

Here you will find some tips n tricks around python.

==== List tricks

====== Print a list in one line [source,python] —-

l = [“a”, “b”, “c”] “;”.join(l) ‘a;b;c’

l = [1, 2, 3] ““.join(str(l)) ‘[1, 2, 3]’ —-

====== Get the last elem or go back in a list [source,python] —- l = [“a”, “b”, “c”] print (l[-1]) # Get the last element of the list which will print “c” print (l[-2]) # Will print “b” —-

====== Get all the odd numbers of a list [source,python] —-

l = [0, 1, 2, 3, 4, 5] l[1::2] # start the list at 1 and go +2 on the iterator [1, 3, 5] —- ====== Reverse a full list [source,python] —- l [0, 1, 2, 3, 4, 5] l = l[::-1] l [5, 4, 3, 2, 1, 0] —-

====== Remove duplicates in a list

Using the builtin set() {Sets are unordered collections of distinct objects} we can remove all the duplicates and to go back in a list we can use the list() function.

[source,python]

l1 = [1, 2, 3, 1, 2, 3] l1 = set(l1) l1 set([1, 2, 3]) l1 = list(l1) l1 [1, 2, 3] —- ====== string list to int list in one line [source,python] —- l = [“1”, “2”, “3”] l = [int(x) for x in l] l [1, 2, 3] —-

====== Remove empty string in a list

[source,python]

l = [“a”, “”, “b”] l [‘a’, ‘’, ‘b’] l = [x for x in l if x] l [‘a’, ‘b’] —-

==== Ternary in python Added in 2.5 version of python :

[source,python]

a = 1 b = 2 result = 0

result = a if a > b else b print (result) # will print 2 for b

result = a if a < b else b print (result) # will print 1 for a

#<1>

####

def yes(): print “yes”

def no(): print “no”

yes() if True else no() yes() if False else no()

#<2>

---

<1> Will output :

2 1

<2> Will output :

yes no

==== Syntax *

The single star * unpacks the sequence/collection into positional arguments.

[source,python]

def sum(a, b): return a + b

values = (1, 2)

s = sum(*values) # will return the sum of 1 and 2

==== Multilines import

A nice way to import

[source, python]

from Package.class import( method1, method2, ) —-

==== How to check if a file with extension .xx is in a folder

[source, python]

from os import listdir from os.path import isfile, join

lFilesList = [f for f in listdir(self.__fileName) if isfile(join(self.__fileName, f)) and (join(self.__fileName, f)).endswith(“.sda”)] if len(lFilesList) > 0: print “There are files” —-

==== Get items from a list a if not in b

Use set(b) instead of b, why ? List membership testing is O(n), Set membership testing is O(1)

So if you test list membership in a loop the overall loop is O(n2).

[source, python]

a = [1, 2, 3, 4 ,5] b = [4, 5, 6, 7]

res = [x for x in a if x not in set(b)]

now res is : [1, 2, 3]

---

==== How to check the method existing in a python object

[source, python]

[method_name for method_name in dir(object) if callable(getattr(object, method_name))] —-

==== Format text

[source, python]

s = “hello world” s.center(40) ‘ hello world ‘

’‘.format(‘sample text’) ‘******sample text*******’ # * is the fill character.

’‘.format(‘sample text’) ‘ sample text ‘ # with a length of 50.

x = 13.949999999999999999 x 13.95 g = float(“{0:.2f}”.format(x)) g 13.95 x == g True h = round(x, 2) h 13.95 x == h True —-

==== script with arguments

Use click library : http://click.pocoo.org/5/