Python Flashcards
change a tuple
illegal
add element to list
a.append(elem)
add two lists
a + [1, 3]
get last list element
a[-1]
copy index 1, 2 and 3 to sublist
a[1:4]
delete element with a given index
del a[i]
remove an element with a given value
a.remove(value)
find index corresponding to an element’s value
a.index(value)
test if a value is contained in the list
value in a
count how many elements that have given value
a.count(value)
number of elements in list a
len(a)
the smallest element in a
min(a)
the largest element in a
max(a)
add all elements in a
sum(a)
sort list
a.sort() # changes a
sort list into a new list
sorted(a)
reverse list
a.reverse() # changes a
check if a is a list
isinstance(a, list)
Print full names
names = ["Ola", "Per", "Kari"] surnames = ["Olsen", "Pettersen", "Bremnes"]
for name, surname in zip(names, surnames):
print name, surname
Print indexes and names
names = [“Ola”, “Per”, “Kari”]
for i, name in enumerate(names):
print i, name
evaluate string expressions
r = eval(‘x + 2.2’)
read a file
file = open(filename, ‘r’)
for line in file:
print line
infile.close()
write to file
file = open(filename, ‘w’) # or ‘a’ to append
file.write(“””
….
“””)
initialize a dictionary
a = {'point': [2,7], 'value': 3}
a = dict(point=[2,7], value=3)add new key-value pair to a dictionary
a[‘key’] = value
delete a key-value pair from the dictionary
del a[‘key’]
list of keys in dictionary
a.keys()
list of values in dictionary
a.values()
number of key-value pairs in dictionary
len(a)
loop over keys in unknown order
for key in a:
loop over keys in alphabetic order
for key in sorted(a.keys()):
check if a is a dictionary
isinstance(a, dict)
get index of char in string
str.find(‘char’)
split string into substrings
str.split(‘:’)
test if substring is in string
substring in string
remove leading/trailing blanks
str.strip()
combine list into string with delimiter
’, ‘.join(list)
file blogging
import glob
files = glob.glob(‘*.pdf’)
check for directory
import os.path
os.path.isdir(myfile)
get file size
import stat
os.stat(myfile)[stat.ST_SIZE]
copy a file
import shutil
shutil.copy(myfile, newfile)
rename a file
import os
os.rename(myfile, ‘newname’)
remove a file
import os
os.remove(‘filename’)
create directory
os.mkdir(dirname)
create path out of strings
os.path.join(os.environ[‘HOME’], ‘py’, ‘src’)
remove directory
shutil.rmtree(‘myroot’)
get filename out of full path
os.path.basename(path)
traverse directory
def myfunc(arg, dirname, files):
for filename in files:
arg.append(filename)
os.path.walk(os.environ['HOME'], myfunc, list)
for filename in list:
print filenameprint with variables
print ‘%d: %s’ % (index, string)
a = [1, 2]
b = a
a is b?
True
make a copy of list
b = a[:]
make a copy of dictionary
b = a.copy()
run stand-alone application
from subprocess import Popen, PIPE
p = Popen(cmd, shell=True, stdout=PIPE)
output, errors = p.communicate()
read file into a list of lines
file = open(filename, 'r') lines = file.readlines()
convert string to float
float(str)
boolean type
bool a = True
convert all elements in list to float
y = map(float, y)
define comparison criterion
def comparator(s1, s2):
# return -1, 0, 1
list.sort(comparator)replace in string
str.replace(this, withThis)
multi-line string
str = “””
…
“””
substring fra string
string[1:5]
Are string mutable?
No, strings (and tuples) are immutable
change global variables inside function
global varName
main-function
if __name__ == ‘__main__’:
doc string
first string in functions, classes, files
print doc string
> > > print function.__doc__
doctest
Inside doc string: """ >>> function(3) 6.0 """
import doctest
doctest.testmod(function)
run doctest
Just run the script!
import doctest
doctest.testmod(function)
define class w/ constructor
class MyClass(object):
conter = 0 # static variable
def \_\_init\_\_(self, i): # constructor
self.i = i;create object of class
obj = MyClass(5)
define subclass
class SubClass(MyClass):
def \_\_init\_\_(self, i, j):
MyClass.\_\_init\_\_(self, i)
self.j = jpublic, protected, private
a = # public _b = # non-public \_\_c = # private
class instance: dictionary of user-defined attributes
instance.__dict__
class name from instance
instance.__class__.__name__
list names of all methods and attributes in class instance
dir(instance)
difference between is and ==
is checks object identity
== checks for equal contents
when is a evaluated as true?
if a has
__len__ or
__nonzero__
and the return value is 0 or False
list of local variables
list of global variables
locals()
global()
simple timer
import timeit
print timeit.timeit(function, number=100)
profiler
import profile
profile = profile.run(“func()”)
save profiling data to file, read afterwards
import profile
profile = profile.run(“func()”, “result.txt”)
import pstats
data = pstats.Stats(“result.txt”)
data.print_stats()
