diff --git a/.travis.yml b/.travis.yml
new file mode 100644
index 0000000..b9e1f1c
--- /dev/null
+++ b/.travis.yml
@@ -0,0 +1,26 @@
+language: python
+python:
+  - "3.6"
+before_install:
+  - sudo apt-get update 
+  - sudo apt-get install -y python python3
+script:
+  - |
+    set -e
+
+    for file in $(ls *.py); do
+        echo "Executing with Python 2: $file"
+        python2 $file
+        echo "Executing with Python 3: $file"
+        python3 $file
+    done
+    
+    for file in $(ls *.py2); do
+        echo "Executing with Python 2: $file"
+        python2 $file
+    done
+    
+    for file in $(ls *.py3); do
+        echo "Executing with Python 3: $file"
+        python3 $file
+    done 
diff --git a/CONTRIBUTORS b/CONTRIBUTORS
index 0269a06..87521dd 100644
--- a/CONTRIBUTORS
+++ b/CONTRIBUTORS
@@ -35,3 +35,4 @@
 - flint (github.com/flintforge)
 - kazuhiko (github.com/JohnTitor00)
 - sfdye (github.com/sfdye)
+- ofek (https://github.com/ofek)
diff --git a/README.md b/README.md
index 9ee9c56..734a11f 100644
--- a/README.md
+++ b/README.md
@@ -1,3 +1,5 @@
+[![Build Status](https://travis-ci.org/brennerm/PyTricks.svg?branch=master)](https://travis-ci.org/brennerm/PyTricks)
+
 ## Intention
 Creating a knowledge base of unpopular Python built-in features to save a lot of unnecessary code.
 
diff --git a/argumentunpacking.py b/argumentunpacking.py
old mode 100755
new mode 100644
index 78c86ef..c474851
--- a/argumentunpacking.py
+++ b/argumentunpacking.py
@@ -3,8 +3,18 @@
 def product(a, b):
     return a * b
 
-argument_tuple = (1, 1)
-argument_dict = {'a': 1, 'b': 1}
+def fn_iterable():
+    return [2, 3]
+
+def fn_dict():
+    return {'a': 2, 'b': 3}
+
+argument_tuple = (2, 3)
+argument_dict = {'a': 2, 'b': 3}
 
 print(product(*argument_tuple))
 print(product(**argument_dict))
+
+# unpacking works as well on function return values
+print(product(*fn_iterable()))
+print(product(**fn_dict()))
diff --git a/boolasint.py b/boolasint.py
old mode 100755
new mode 100644
diff --git a/boolfast.py b/boolfast.py
new file mode 100644
index 0000000..c1a71ad
--- /dev/null
+++ b/boolfast.py
@@ -0,0 +1,38 @@
+"""Getting the truthyness via bool(obj) is slow because it is a global and
+therefore involves multiple namespace lookups. You can use the keyword `not`
+to avoid the overheard i.e. `not not obj`.
+"""
+
+import timeit
+
+slow_setup = """
+class C:
+    def __init__(self):
+        self.some_val = 5
+    def __bool__(self):
+        return bool(self.some_val)
+a = C()
+"""
+
+fast_setup = """
+class C:
+    def __init__(self):
+        self.some_val = 5
+    def __bool__(self):
+        return not not self.some_val
+a = C()
+"""
+
+# on my machine:
+
+# 0.433618037256565
+print(timeit.timeit('a.__bool__()', slow_setup))
+
+# 0.2220980115553175
+print(timeit.timeit('a.__bool__()', fast_setup))
+
+# 0.40519480762077364
+print(timeit.timeit('if a:pass', slow_setup))
+
+# 0.24311949953334988
+print(timeit.timeit('if a:pass', fast_setup))
diff --git a/boolisslow.py b/boolisslow.py
index b2c430d..2d80ff3 100644
--- a/boolisslow.py
+++ b/boolisslow.py
@@ -7,12 +7,12 @@
 
 Note: This leads to a performance improvement only in Python2.
 """
-
+import sys
 from timeit import timeit
 
 
 def test_true():
-    count = 1000
+    count = 100
     while True:  # here is True
         if count < 0:
             break
@@ -20,23 +20,14 @@ def test_true():
 
 
 def test_1():
-    count = 1000
+    count = 100
     while 1:  # here is 1
         if count < 0:
             break
         count -= 1
 
 
-# on my macbook pro 15
-# test_true is about 59.3047289848 seconds
-# test_1 is about 39.0966179371 seconds
+# test_true is about 5.01579904556 seconds
+# test_1 is about 3.70646500587 seconds
 print(timeit(test_true, number=1000000))
 print(timeit(test_1, number=1000000))
-
-
-# True and False can be changed in python2
-True = 0
-False = 100
-
-print(True)
-print(False)
diff --git a/boolisslow.py2 b/boolisslow.py2
new file mode 100644
index 0000000..cae74e9
--- /dev/null
+++ b/boolisslow.py2
@@ -0,0 +1,6 @@
+# True and False can be changed in python2
+True = 0
+False = 100
+    
+print(True)
+print(False)
diff --git a/cacheproperty.py b/cacheproperty.py
index 562fc27..20742d6 100644
--- a/cacheproperty.py
+++ b/cacheproperty.py
@@ -1,4 +1,4 @@
-class PropertyCache:
+class PropertyCache(object):
     """ a decorator to cache property
     """
 
diff --git a/calculator.py b/calculator.py
old mode 100755
new mode 100644
index 882e2b2..8dbe394
--- a/calculator.py
+++ b/calculator.py
@@ -12,11 +12,8 @@
     "+": operator.add,
     "-": operator.sub,
     "/": operator.truediv,
-    "*": operator.mul
+    "*": operator.mul,
+    "**": pow
 }
 
-x = input("Enter an operator [OPTIONS: +, -, *, /]: ")
-y = int(input("Enter number: "))
-z = int(input("Enter number: "))
-
-print (ops[x](y, z))
+print(ops['-'](50, 25))
diff --git a/chainedcomparison.py b/chainedcomparison.py
old mode 100755
new mode 100644
diff --git a/concatenatestrings.py b/concatenatestrings.py
old mode 100755
new mode 100644
diff --git a/conditionalassignment.py b/conditionalassignment.py
old mode 100755
new mode 100644
diff --git a/conditionalfunctioncall.py b/conditionalfunctioncall.py
old mode 100755
new mode 100644
diff --git a/contextmanagers.py b/contextmanagers.py
index 138c6d9..021de87 100644
--- a/contextmanagers.py
+++ b/contextmanagers.py
@@ -12,29 +12,26 @@
 
 @contextlib.contextmanager
 def unlock(resource):
-    resource = "unlocked"
+    resource.locked = False
     try:
-        yield resource
+        yield
     finally:
-        resource = "locked"
+        resource.locked = True
 
 
 # a resource that is locked
-resource = "locked" 
+class Resource:
+  def __init__(self):
+    self.locked = True
+
+resource = Resource()
 
 # test that it is indeed locked
-print(resource)
+print(resource.locked)
 
 # call your 'unlock' context manager with your resource
-with unlock(resource) as unlocked:
-    print(unlocked) # check that it is unlocked
+with unlock(resource):
+    print(resource.locked) # check that it is unlocked
 
 # ensure it was re-locked when it left the 'unlock' context
-print(resource)
-
-
-
-
-
-
-
+print(resource.locked)
diff --git a/controlwhitespaces.py b/controlwhitespaces.py
old mode 100755
new mode 100644
diff --git a/copylist.py b/copylist.py
old mode 100755
new mode 100644
index d503efc..c8b9afe
--- a/copylist.py
+++ b/copylist.py
@@ -1,10 +1,18 @@
 #! /usr/bin/env python3
+import sys
+
 """a fast way to make a shallow copy of a list"""
 
 a = [1, 2, 3, 4, 5]
 print(a[:])
 
 
+"""adding an empty list yields a copy of initial list"""
+
+a = [1, 2, 3, 4, 5]
+print(a + [])  # in python3, for small lists performs faster than a[:]
+
+
 """copy list by typecasting method"""
 
 a = [1, 2, 3, 4, 5]
@@ -13,9 +21,14 @@
 
 """using the list.copy() method (python3 only)"""
 
-a = [1, 2, 3, 4, 5]
-
-print(a.copy())
+if sys.version_info.major == 3:
+    a = [1, 2, 3, 4, 5]
+    print(a.copy())
+else:
+    # in python2 there exists the `copy` builtin module
+    from copy import copy
+    a = [1, 2, 3, 4, 5]
+    print(copy(a))
 
 
 """copy nested lists using copy.deepcopy"""
diff --git a/dictionaryget.py b/dictionaryget.py
old mode 100755
new mode 100644
diff --git a/dictsortbyvalue.py b/dictsortbyvalue.py
old mode 100755
new mode 100644
diff --git a/dictswapkeysvalues.py b/dictswapkeysvalues.py
old mode 100755
new mode 100644
diff --git a/exec.py b/exec.py
old mode 100755
new mode 100644
diff --git a/extendediterableunpacking.py b/extendediterableunpacking.py3
old mode 100755
new mode 100644
similarity index 90%
rename from extendediterableunpacking.py
rename to extendediterableunpacking.py3
index bc5d77f..88014be
--- a/extendediterableunpacking.py
+++ b/extendediterableunpacking.py3
@@ -1,4 +1,3 @@
-#! /usr/bin/env python3
 """allows collecting not explicitly assigned values into 
 a placeholder variable"""
 
diff --git a/flattenlist.py b/flattenlist.py
old mode 100755
new mode 100644
index 51070d6..a086ce9
--- a/flattenlist.py
+++ b/flattenlist.py
@@ -1,4 +1,3 @@
-#! /usr/bin/env python3
 """
 Deep flattens a nested list
 
@@ -10,18 +9,6 @@
 """
 
 
-def flatten_list(L):
-    for item in L:
-        if isinstance(item, list):
-            yield from flatten_list(item)
-        else:
-            yield item
-
-# In Python 2
-from compiler.ast import flatten
-flatten(L)
-
-
 # Flatten list of lists
 
 a = [[1, 2], [3, 4]]
@@ -35,8 +22,5 @@ def flatten_list(L):
 
 print(list(itertools.chain.from_iterable(a)))
 
-# In Python 2
-print(reduce(lambda x, y: x+y, a))
-
 print(sum(a, []))
 
diff --git a/flattenlist.py2 b/flattenlist.py2
new file mode 100644
index 0000000..32d144a
--- /dev/null
+++ b/flattenlist.py2
@@ -0,0 +1,7 @@
+L = [1, 2, [3, 4], [5, 6, [7]]]
+
+from compiler.ast import flatten
+flatten(L)
+
+a = [[1, 2], [3, 4]]
+print(reduce(lambda x, y: x+y, a))
\ No newline at end of file
diff --git a/flattenlist.py3 b/flattenlist.py3
new file mode 100644
index 0000000..15c9bbf
--- /dev/null
+++ b/flattenlist.py3
@@ -0,0 +1,10 @@
+L = [1, 2, [3, 4], [5, 6, [7]]]
+
+def flatten(L):
+    for item in L:
+        if isinstance(item, list):
+            yield from flatten(item)
+        else:
+            yield item
+
+flatten(L)
diff --git a/forelse.py b/forelse.py
old mode 100755
new mode 100644
diff --git a/ifelsecommentswitch.py b/ifelsecommentswitch.py
old mode 100755
new mode 100644
diff --git a/keydefaultdict.py b/keydefaultdict.py
index af4fede..3f0ece0 100644
--- a/keydefaultdict.py
+++ b/keydefaultdict.py
@@ -1,5 +1,5 @@
 """
-keydefaultdict with where the function recieves the key.
+keydefaultdict with where the function receives the key.
 """
 from collections import defaultdict
 
diff --git a/loopoverlappingdicts.py b/loopoverlappingdicts.py
old mode 100755
new mode 100644
index e7d5dda..c6b1b31
--- a/loopoverlappingdicts.py
+++ b/loopoverlappingdicts.py
@@ -6,11 +6,3 @@
 
 for ky in set(dctA) & set(dctB):
     print(ky)
-
-"""loop over dicts that share (some) keys in Python3"""
-for ky in dctA.keys() & dctB.keys():
-    print(ky)
-
-"""loop over dicts that share (some) keys and values in Python3"""
-for item in dctA.items() & dctB.items():
-    print(item)
diff --git a/loopoverlappingdicts.py3 b/loopoverlappingdicts.py3
new file mode 100644
index 0000000..ef2646a
--- /dev/null
+++ b/loopoverlappingdicts.py3
@@ -0,0 +1,11 @@
+#! /usr/bin/env python3
+dctA = {'a': 1, 'b': 2, 'c': 3}
+dctB = {'b': 4, 'c': 3, 'd': 6}
+
+"""loop over dicts that share (some) keys in Python3"""
+for ky in dctA.keys() & dctB.keys():
+    print(ky)
+
+"""loop over dicts that share (some) keys and values in Python3"""
+for item in dctA.items() & dctB.items():
+    print(item)
diff --git a/maxsplit.py b/maxsplit.py
old mode 100755
new mode 100644
diff --git a/merge_dict.py b/merge_dict.py
index 832096f..80d4df0 100644
--- a/merge_dict.py
+++ b/merge_dict.py
@@ -1,13 +1,7 @@
-#! /usr/bin/env python3.5
 """merge dict's"""
 
 d1 = {'a': 1}
 d2 = {'b': 2}
 
-#  python 3.5
-print({**d1, **d2})
-
-print(dict(d1.items() | d2.items()))
-
 d1.update(d2)
 print(d1)
diff --git a/merge_dict.py3 b/merge_dict.py3
new file mode 100644
index 0000000..086e677
--- /dev/null
+++ b/merge_dict.py3
@@ -0,0 +1,8 @@
+"""merge dict's"""
+
+d1 = {'a': 1}
+d2 = {'b': 2}
+
+print({**d1, **d2})
+
+print(dict(d1.items() | d2.items()))
\ No newline at end of file
diff --git a/metatable.py b/metatable.py
index 040079c..caec968 100644
--- a/metatable.py
+++ b/metatable.py
@@ -1,5 +1,5 @@
 """
-metatable with where the function recieves the dictionary and key.
+metatable with where the function receives the dictionary and key.
 """
 from collections import defaultdict
 
diff --git a/namedformatting.py b/namedformatting.py
old mode 100755
new mode 100644
index ceda335..6e075ba
--- a/namedformatting.py
+++ b/namedformatting.py
@@ -23,9 +23,4 @@ class Person:
 me.name = 'Jeff'
 me.email = 'jeff@usr.com'
 me.phone = '919-123-4567'
-print('My name is {me.name}, my email is {me.email} and my phone number is {me.phone}'.format(me=me))
-
-"""f-string (Python 3.6+)"""
-name = "Jeff"
-age = 24
-print(f"My name is {name} and I'm {age} years old.")
+print('My name is {me.name}, my email is {me.email} and my phone number is {me.phone}'.format(me=me))
\ No newline at end of file
diff --git a/namedformatting.py3 b/namedformatting.py3
new file mode 100644
index 0000000..04e5ac4
--- /dev/null
+++ b/namedformatting.py3
@@ -0,0 +1,4 @@
+"""f-string (Python 3.6+)"""
+name = "Jeff"
+age = 24
+print(f"My name is {name} and I'm {age} years old.")
\ No newline at end of file
diff --git a/removeduplicatefromlist.py b/removeduplicatefromlist.py
old mode 100755
new mode 100644
diff --git a/reverselist.py b/reverselist.py
old mode 100755
new mode 100644
diff --git a/setglobalvariables.py b/setglobalvariables.py
old mode 100755
new mode 100644
diff --git a/setoperators.py b/setoperators.py
old mode 100755
new mode 100644
diff --git a/socketmsghandling.py b/socketmsghandling.py
index c315b4c..94508fd 100644
--- a/socketmsghandling.py
+++ b/socketmsghandling.py
@@ -1,19 +1,23 @@
 import socket
 import functools
 
-s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
-conn = s.connect(('localhost', 80))
-msgs = []
+ConnectionRefusedError = socket.error
 
-# normal way
-# while True:
-#    msg = coon.recv(1024)
-#    if recv:
-#        msgs.append(msg)
-# else:  # when no msg come, break
-#         break
+msgs = []
+s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+try:
+    conn = s.connect(('localhost', 80))
+    # normal way
+    # while True:
+    #    msg = coon.recv(1024)
+    #    if recv:
+    #        msgs.append(msg)
+    # else:  # when no msg come, break
+    #         break
 
-# hack way with iter and functools.partial
-# this circle will auto break when msg is empty ''
-for msg in iter(functools.partial(conn.recv, 1024), b''):
-    msgs.append(msg)
+    # hack way with iter and functools.partial
+    # this circle will auto break when msg is empty ''
+    for msg in iter(functools.partial(conn.recv, 1024), b''):
+        msgs.append(msg)
+except (socket.error, ConnectionRefusedError):
+    pass
\ No newline at end of file
diff --git a/stepslice.py b/stepslice.py
old mode 100755
new mode 100644
diff --git a/switch_case_statments_with_dict.py b/switch_case_statments_with_dict.py
old mode 100755
new mode 100644
diff --git a/valueswapping.py b/valueswapping.py
old mode 100755
new mode 100644
index 1f18a66..70011c8
--- a/valueswapping.py
+++ b/valueswapping.py
@@ -1,6 +1,11 @@
 #! /usr/bin/env python3
-"""pythonic way of value swapping"""
+# Type of variable: Number
 a, b = 5, 10
 print(a, b)
 a, b = b, a
 print(a, b)
+# Type of variable: List
+myList = [1, 2, 3, 4, 5]
+print("Initial Array :", myList)
+myList[0], myList[1] = myList[1], myList[0]
+print("Swapped Array :", myList)
diff --git a/whileelse.py b/whileelse.py
old mode 100755
new mode 100644