Python For C++ Developers

Check is something empty
Don’t forget : at the end
Use pass if nothing to do in a branch
NULL/true/false
Logic operators
Indention
for each
Enumerate items in a container
string
Join strings
Swap two variables
list, set, tuple, dict
List comprehension
Ternary operator
Reference or Value

Tips for C++ developers jump to use Python.

Check is something empty

it is recommended to use

if items:
  do some thing

other than

if len(items) != 0: 
  do some thing
if items != None: 
  do some thing

Don’t forget `:` at the end

Python uses : to indicate a block of code. Although I think it is not necessary, but it is.

if some_condition:
  do something
while some_condition:
  do something

Use `pass` if nothing to do in a branch

if some_condition:
  pass
else:
  do something

NULL/true/false

Use ‘None/True/False’ instead.

Logic operators

Use and, or, not for && || ! respectively

if not some_condition:
  pass
if some_condition and another_condtion:
  pass

Indention

Indention in python is non-trivial and compulsory. Code-block is defined by indention like { and } in C++

if some_condition:
  do something
  do another thing # OK, indention is consistent with the previous statement
else:
  do something else
    do another thing # Fails since the indention is inconsistent

Be caution with tab and space. It is recommended to config your editor display white-chars and replace tab with spaces.

for each

for item in item_list:
  print item

Enumerate items in a container

for (index, item) in enumerate(items): 
  print index, item

for (key,value) in mydict.items():
  print key,value

string

'this is a string'
"this is also a string"
'''this is a 
multi-line string'''

Join strings

colors = ['red', 'blue', 'green', 'yellow'] 
result = '|'.join(colors)
print result #It will print 'red|blue|green|yellow' 

Swap two variables

a,b = b,a

list, set, tuple, dict

list -> array/vector: ['this','is','a','list']
set -> std::set
tuple -> const list: ('this','is','a','list')
dict -> hash map: {"key1":"value1", "key2":"value2"}

list to set: aNewSet = set(mylist), with duplicated item automatically removed set to list: aNewList = list(myset) list to tuple: aNewTuple = tuple(mylist) tuple to list: aNewList = list(mytuple)

List comprehension

result = [x for x in xrange(10) if x % 2 == 0]
print result #will be 2 4 6 8

Ternary operator

a = 1 if some_condition else 2

Reference or Value

Every object is a reference to memory. python will collect an object if there is no reference to it.

you can use copy to clone a object

import copy
#simple copy, like in C++, just copy it if there is no pointer member
aNewList = copy.copy(theOldList)
#like in C++, deep copy is required if there's any pointer member
aNewList = copy.deepcopy(theOldList) 