Built-In data types
None |
NoneType |
None object |
bool |
Boolean |
True, False |
int |
Integer |
-2, -1, 0, 1, 2 |
long |
Long Integer |
123456789012345L |
float |
Floating point |
3.1415 |
complex |
complex |
3 + 4*1j |
str |
String |
'alice', 'bob' |
unicode |
Unicode String |
u'alice', u'bob' |
list |
List |
[1, 'two', 3.0] |
tuple |
Tuple |
(1, 'two', 3.0) |
dict |
Dictionary |
{'name': alice, 'age': 7} |
Indentation matters
if Cheshire.is_visible:
print('I can see you')
alice.talks()
else:
print("I can't see you")
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Four spaces is the recommended by PEP 8 (Style Guide for Python Code)
String Literals
'alice'
"bob"
"The Hatter's Tea"
"""Twinkle, twinkle, little bat!
How I wonder what you're at!"""
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String Methods
s.lower() |
Lowercased copy |
s.upper() |
Uppercased copy |
s.isalpha() |
True if alphabetic |
s.isalnum() |
True if alphanumeric |
s.split(t) |
Split s using t as separator |
s.zfill(w) |
Padding with leading zeros |
s.strip() |
Removes beg/end spaces |
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Lists
lst.append(x) |
Append x to the end of lst |
lst.count(x) |
How many times x is in lst |
lst.extend(itr) Same as lst += itr |
Append all of iterable itr to lst |
lst.index(x) |
Index position of the first occurrence |
lst.insert(i,x) |
Insert item x into lst at index i |
lst.pop() |
Removes the last item in lst |
lst.pop(i) |
Removes item with index i |
lst.remove(x) |
Removes the first occurrence of x in lst |
lst.reverse() |
Reverse the list lst in-place |
lst.sort() |
Sorts lst in-place |
List Comprehensions
>>> [2**x for x in range(10)]
[1, 2, 4, 8, 16, 32, 64, 128, 256, 512]
>>> [2**x for x in range(10) if x%2 == 0]
[1, 4, 16, 64, 256]
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Dictionaries
d.clear() |
All items from dict d |
d.copy() |
Shallow copy of dict d |
d.keys() |
Read-only iterable of all keys |
d.values() |
Read-only iterable of all values |
d.items() |
Read-only iterable of all (key, value) |
d.pop(k) |
Removes (k, value) and returns d[k] |
Conditionals
if x > 0 and y > 0:
print('First Quadrant')
elif x < 0 and y > 0:
print('Second Quadrant')
elif y < 0:
print('Third and Fourth')
else:
print('On the axis')
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Loops (for)
a=1
b=2
for i in range(10):
c=a+b
print c
a=b; b=c
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Loops (while)
import random
x=1.0
while True:
x*=random.random()
print x
if x<0.5:
x*=3
continue
if x>0.8:
break
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You can use 'break' to escape from the inner loop and 'continue' to jump to the next item in the loop
Classes
class Quaternion(object):
def __init__(self, four_tuple):
self.values=four_tuple
@property
def real(self):
return self.values[0]
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Special Methods
__bool__(self) |
True of False return |
__init__(self, args) |
Object Initialization |
__hash__(self) |
To be use as key |
__repr__(self) |
String eval(repr(x))==x |
__str__(self) |
Human readable string |
Comparison Special Methods
__lt__(self, other) |
< |
__le__(self, other) |
<= |
__gt__(self, other) |
> |
__ge__(self, other) |
>= |
__eq__(self, other) |
== |
__ne__(self, other) |
!= |
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os Module
os.listdir(path) |
Equivalent to 'ls' |
os.getcwd() |
Current Working Directory (pwd) |
os.mkdir(path) |
Make directory (mkdir) |
os.chdir(path) |
Change directory (cd) |
os.path.isfile(path) |
Check if path is a file |
os.path.isdir(path) |
Check if path is directory |
os.path.exists(path) |
Check existence as file or directory |
sys Module
sys.argv |
List of arguments |
sys.version |
Python version |
sys.platform |
OS platform |
sys.maxint |
Max integer |
sys.stdout |
Standard output |
sys.stderr |
Standard error |
itertools Module
product('ABCD', repeat=2) |
AA AB AC AD BA BB BC BD CA CB CC CD DA DB DC DD |
permutations('ABCD', 2) |
AB AC AD BA BC BD CA CB CD DA DB DC |
combinations('ABCD', 2) |
AB AC AD BC BD CD |
combinations_with_replacement('ABCD', 2) |
AA AB AC AD BB BC BD CC CD DD |
math Module
sin, cos, tan |
Trigonometrical |
asin, acos, atan |
Inv. Trigonometrical |
sinh, cosh, tanh |
Hyperbolic |
asinh, acosh, atanh |
Inverse Hyperbolic |
ceil, floor, trunc |
Truncation |
log, log10 |
Logarithms |
sqrt, exp, pow |
Exponentials |
degrees, radians |
Angular conversion |
pi, e |
Math Constants |
json Module
>>> import json
>>> dic={'name':'Alice', 'age': 7.5}
>>> dic_json=json.dumps(dic,
sort_keys=True,
indent=4,
separators=(',', ': '))
>>> print dic_json
{
"age": 7.5,
"name": "Alice"
}
>>> dic2=json.loads(dic)
>>> dic2
{u'age': 7.5, u'name': u'Alice'}
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