Python Language & Syntax Cheat Sheet
Python is white-space dependent; code blocks are indented 4 spaces (not tabs)
Variable Assignment
integer = 1
string = “string”
unicode_string = u”unicode string”
mutli_line_string = “““ multi-line
string
”””
tuple = (element1, element2, element3, …)
list = [ element1, element2, element3, ... ]
dictionary = { key1 : value1, key2 : value2, ... }
dictionary[key] = value
class_instance = ClassName(init_args)
Frequently Used Built-in Types
True False None
str unicode int
float list dict
Other than True, False and None, these can also be used as
functions to explicitly cast a value to that type
Functions
def function_name(arg1, arg2,
keyword1=val1, keyword2=val2, ...):
<function body>
return return_value
e.g.
def my_function(x, y, z=0):
sum = x + y + z
return sum
my_function(1, 2) → 3
my_function(1, 2, 3) → 6
my_function(1, 2, y=4) → 7
Classes
class ClassName(SuperClass):
class_variable = static_value
def __init__(self, value1, <...>):
self.instance_variable1 = value1
self.instance_function()
def instance_function(self, arg1, <...>):
<function body>
return return_value
e.g.
class MyClass(object):
offset = 1
def __init__(self, value):
self.value = value
def get_offset_value(self):
return MyClass.offset +
self.value
MyClass.offset → 1
c = MyClass(2)
c.value → 2
c.get_offset_value() → 3
Imports
import module
from module import class, function, variable
Frequently Used String Manipulations
string1 + string1 “str” + “ing” → “string”
"%s%s" % (string1, string2) “%s%s” % (“s”, “g”) → “sg”
string.split("delim", limit) “s/g”.split(“/”) → [“s”, “g”]
string.strip() “ string “.strip() → “string”
string.startswith("prefix") “str”.startswith(“s”) → True
substring in string “str” in “string” → True
print string
List Comprehension
[ value for value in list if condition ]
e.g.
[x for x in [1,2,3,4,5,6,7,8,9] if x % 2 == 0] → [2,4,6,8]
Accessing Variable Values
value = dictionary[key]
value = dictionary.get(key, default_value)
value = list[index] e.g. [5,6,7][2] → 7
value = string[start:end] e.g “string”[0:3] → “str”
value = list[start:end] e.g. [1,2,3][1:2] → [2]
value = ClassName.class_variable
value = class_instance.instance_variable
value = class_instance.function(args)
Comparisons
value1 == value2 “str” == “str” → True
value1 != value2 “str” != “str” → False
value1 < value2 1 < 2 → True
value1 <= value2 2 <= 2 → True
value1 > value2 2 > 3 → False
value1 >= value2 3 >= 3 → True
value is [not] None
value in list 1 in [2,3,4] → False
isinstance(class_instance, ClassName)
Basic Arithmetic
i = a + b i = a - b
i = a / b i = a * b
i = a % b e.g. 11 % 3 → 2
Comments
"""
Multi-line comment
"""
# Line Comment
Control Flow
if conditional:
<body>
elif conditional:
<body>
else:
<body>
e.g.
if i == 7:
print “seven”
elif i == 8:
print “eight”
else:
print str(i)
for value in list:
<body>
continue
break
e.g.
for i in [1, 2, 3, 4]:
if i == 2: continue
if i == 3: break
print i
while conditional:
<body>
continue
break
e.g.
while True:
print “infinity”
Exceptions
try:
<body>
raise Exception()
except Exception as e:
<exception handling>
finally:
<clean-up>
e.g.
try:
database.update()
except Exception as e:
log.error(e.msg)
database.abort()
finally:
database.commit()
File & Path Manipulation
import os # import the os module first
os.path.join(path_segment1, path_segment2, ...)
os.path.exists(path)
os.listdir(directory_path)
os.remove(file_path)
os.rmdir(directory_path)
file = open(path, "rw")
file.read()
string.write("string")
