Python

Question 1

What is a good way to ensure certain conditions are impossible in your app?

Answer 1

Use assertions!

\>\>\> **def** apply\_discount(price, discount):...**assert** discount \<= 100, 'Whoa! Were not paying people to take our merchandise!'...**return** price \* discount ...\>\>\> apply\_discount(14700, 50)735000\>\>\> apply\_discount(14700, 200) Traceback (most recent call last):File "", line 1, **in** \<module\>File "", line 2, **in** apply\_discount AssertionError: Whoa! Were **not** paying people to take our merchandise!

Remember that assertions can be disabled at runtime, so don’t use them to enforce rules.

Question 2

Explain these Python naming conventions:

• Single Leading Underscore: _var
• Single Trailing Underscore: var_
• Double Leading Underscore: __var
• DoubleLeadingandTrailingUnderscore:__var__
• Single Underscore: _

Answer 2

• Single Leading Underscore “_var”: Naming convention indi- cating a name is meant for internal use. A hint for programmers and not enforced by the interpreter (except in wildcard imports.)
• Single Trailing Underscore “var_”: Used by convention to avoid naming conflicts with Python keywords.
• Double Leading Underscore “__var”: Triggers name man- gling when used in a class context. Enforced by the Python interpreter.
• Double Leading and Trailing Underscore “__var__”: Indi- cates special methods defined by the Python language. Avoid this naming scheme for your own attributes.
• Single Underscore “_”: Sometimes used as a name for tempo- rary or insignificant variables (“don’t care”). Also, it represents the result of the last expression in a Python REPL session.

Question 3

What are the keywords and builtins in Python?

Answer 3

\>\>\> **import** keyword \>\>\> keyword.kwlist ['False', 'None', 'True', 'and', 'as', 'assert', 'async', 'await', 'break', 'class', 'continue','def', 'del', 'elif', 'else', 'except', 'finally', 'for', 'from', 'global', 'if', 'import', 'in','is', 'lambda', 'nonlocal', 'not', 'or', 'pass', 'raise', 'return', 'try', 'while', 'with', 'yield']\>\>\> **import** builtins \>\>\> dir(builtins)['ArithmeticError', 'AssertionError', 'AttributeError', 'BaseException', 'BlockingIOError', 'BrokenPipeError','BufferError', 'BytesWarning', 'ChildProcessError', 'ConnectionAbortedError', 'ConnectionError','ConnectionRefusedError', 'ConnectionResetError', 'DeprecationWarning', 'EOFError', 'Ellipsis', 'EnvironmentError','Exception', 'False', 'FileExistsError', 'FileNotFoundError', 'FloatingPointError', 'FutureWarning','GeneratorExit', 'IOError', 'ImportError', 'ImportWarning', 'IndentationError', 'IndexError', 'InterruptedError','IsADirectoryError', 'KeyError', 'KeyboardInterrupt', 'LookupError', 'MemoryError', 'ModuleNotFoundError','NameError', 'None', 'NotADirectoryError', 'NotImplemented', 'NotImplementedError', 'OSError', 'OverflowError','PendingDeprecationWarning', 'PermissionError', 'ProcessLookupError', 'RecursionError', 'ReferenceError','ResourceWarning', 'RuntimeError', 'RuntimeWarning', 'StopAsyncIteration', 'StopIteration', 'SyntaxError','SyntaxWarning', 'SystemError', 'SystemExit', 'TabError', 'TimeoutError', 'True', 'TypeError', 'UnboundLocalError','UnicodeDecodeError', 'UnicodeEncodeError', 'UnicodeError', 'UnicodeTranslateError', 'UnicodeWarning', 'UserWarning','ValueError', 'Warning', 'ZeroDivisionError', '\_', '\_\_build\_class\_\_', '\_\_debug\_\_', '\_\_doc\_\_', '\_\_import\_\_','\_\_loader\_\_', '\_\_name\_\_', '\_\_package\_\_', '\_\_spec\_\_', 'abs', 'all', 'any', 'ascii', 'bin', 'bool', 'breakpoint','bytearray', 'bytes', 'callable', 'chr', 'classmethod', 'compile', 'complex', 'copyright', 'credits', 'delattr','dict', 'dir', 'divmod', 'enumerate', 'eval', 'exec', 'exit', 'filter', 'float', 'format', 'frozenset', 'getattr','globals', 'hasattr', 'hash', 'help', 'hex', 'id', 'input', 'int', 'isinstance', 'issubclass', 'iter', 'len','license', 'list', 'locals', 'map', 'max', 'memoryview', 'min', 'next', 'object', 'oct', 'open', 'ord', 'pow','print', 'property', 'quit', 'range', 'repr', 'reversed', 'round', 'set', 'setattr', 'slice', 'sorted','staticmethod', 'str', 'sum', 'super', 'tuple', 'type', 'vars', 'zip']

Question 4

How do you get the size of something in memory?

Answer 4

\>\>\> **import** sys \>\>\> size = sys.getsizeof \>\>\> **print**(size('a'), 'bytes in memory')50 bytes **in** memory \>\>\> **print**(size('0'), 'bytes in memory')50 bytes **in** memory \>\>\> **print**(size('10'), 'bytes in memory')51 bytes **in** memory \>\>\> **print**(size('10\*10'), 'bytes in memory')54 bytes **in** memory \>\>\> **print**(size('9999999999999'), 'bytes in memory')62 bytes **in** memory \>\>\> **print**(size('999\*\*999'), 'bytes in memory')57 bytes **in** memory

Question 5

What will this code output? Explain.

\>\>\> **from** collections **import** namedtuple \>\>\> Person = namedtuple('Person', 'first\_name last\_name age')\>\>\> bob = Person('Bob', 'Smith', 47)\>\>\> **print**(f'''... {bob[0]}... {bob.last\_name}... {type(bob)}... ''')

Answer 5

Tuples are great for storing ordered data you don’t want changed, like configuration settings.

But if they get really long, it can get hard to remember which values are in which index. Named Tuples let you name the values:

\>\>\> **from** collections **import** namedtuple \>\>\> Person = namedtuple('Person', 'first\_name last\_name age')\>\>\> bob = Person('Bob', 'Smith', 47)\>\>\> **print**(f'''... {bob[0]}... {bob.last\_name}... {type(bob)}... ''') Bob Smith \<**class**'\_\_main\_\_.Person'\>

Question 6

Elegantly loop through a csv file…

Answer 6

**import** csv **from** collections **import** namedtuple **with** open("data.csv") **as** f: reader = csv.reader(f) top\_row = next(reader) top\_row = [t.lower().split() **for** t **in** top\_row] top\_row = ['\_'.join(t) **for** t **in** top\_row] Data = namedtuple("Data", top\_row) data = [Data(\*r) **for** r **in** reader]**print**(data)#or**import** pandas **as** pd data = pd.read\_csv('data.csv').to\_dict(orient='row')**print**(data)

Question 7

What does this code output? Explain.

\>\>\> line = (1, 2, 3, 4, 5)\>\>\> a, \*b, c = line \>\>\> **print**(f'''... {a}... {b}... {c}... {type(line)}''')

Answer 7

The splat * lets you unpack variables:

\>\>\> line = (1, 2, 3, 4, 5)\>\>\> a, \*b, c = line \>\>\> **print**(f'''... {a}... {b}... {c}... {type(line)}''')1[2, 3, 4]5\<**class**'tuple'\>

Question 8

Find the most common words in some text.

Answer 8

\>\>\> #Get some text ...how about the Zen of Python?... **import** this \>\>\> text = "".join([this.d.get(c, c) **for** c **in** this.s])\>\>\>\>\>\> **from** collections **import** Counter \>\>\> word\_count = Counter(text.split())\>\>\> **print**(word\_count.most\_common(3))[('is', 10), ('better', 8), ('than', 8)]

Question 9

Sort these by last name alphabetically:

‘Daniel Dennett’, ‘Ned Batchelder’, ‘Raymond Hettinger’, ‘Ludwig Wittgenstein’, ‘Brian Jones’, ‘David Beazley’

Answer 9

\>\>\> names = ['Daniel Dennett', 'Ned Batchelder', 'Raymond Hettinger', 'Ludwig Wittgenstein', 'Brian Jones', 'David Beazley']\>\>\> **print**(sorted(names, key=**lambda** name: name.split()[-1].lower()))['Ned Batchelder', 'David Beazley', 'Daniel Dennett', 'Raymond Hettinger', 'Brian Jones', 'Ludwig Wittgenstein']\>\>\>

Question 10

What will this print? Explain.

\>\>\> **print**(f'''... {True}... {True.\_\_class\_\_}... {True.\_\_class\_\_.\_\_bases\_\_}... {True.\_\_class\_\_.\_\_bases\_\_[0]}... {True.\_\_class\_\_.\_\_bases\_\_[0].\_\_bases\_\_}... {True.\_\_class\_\_.\_\_bases\_\_[0].\_\_bases\_\_[0]}... {type(True).\_\_mro\_\_}... ''')

Answer 10

\>\>\> **print**(f'''... {True}... {True.\_\_class\_\_}... {True.\_\_class\_\_.\_\_bases\_\_}... {True.\_\_class\_\_.\_\_bases\_\_[0]}... {True.\_\_class\_\_.\_\_bases\_\_[0].\_\_bases\_\_}... {True.\_\_class\_\_.\_\_bases\_\_[0].\_\_bases\_\_[0]}... {type(True).\_\_mro\_\_}... ''')True\<**class**'bool'\>(\<**class**'int'\>,)\<**class**'int'\>(\<**class**'object'\>,)\<**class**'object'\>(\<**class**'bool'\>, \<**class**'int'\>, \<**class**'object'\>) \<\<-Method Resolution Order

Question 11

How do you figure out where everything is in Python?

Answer 11

\>\>\> **from** pprint **import** pprint \>\>\> **import** sys \>\>\> pprint(sys.path)['','/Library/Frameworks/Python.framework/Versions/3.8/lib/python38.zip','/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8','/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/lib-dynload','/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages']\>\>\> pprint(sys.modules){'\_\_main\_\_': \<module '\_\_main\_\_' (built-**in**)\>,'\_abc': \<module '\_abc' (built-**in**)\>,'\_ast': \<module '\_ast' (built-**in**)\>,'\_bootlocale': \<module '\_bootlocale' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/\_bootlocale.py'\>,'\_codecs': \<module '\_codecs' (built-**in**)\>,'\_collections': \<module '\_collections' (built-**in**)\>,'\_collections\_abc': \<module '\_collections\_abc' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/\_collections\_abc.py'\>,'\_frozen\_importlib': \<module 'importlib.\_bootstrap' (frozen)\>,'\_frozen\_importlib\_external': \<module 'importlib.\_bootstrap\_external' (frozen)\>,'\_functools': \<module '\_functools' (built-**in**)\>,'\_heapq': \<module '\_heapq' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/lib-dynload/\_heapq.cpython-38-darwin.so'\>,'\_imp': \<module '\_imp' (built-**in**)\>,'\_io': \<module 'io' (built-**in**)\>,'\_locale': \<module '\_locale' (built-**in**)\>,'\_opcode': \<module '\_opcode' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/lib-dynload/\_opcode.cpython-38-darwin.so'\>,'\_operator': \<module '\_operator' (built-**in**)\>,'\_posixsubprocess': \<module '\_posixsubprocess' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/lib-dynload/\_posixsubprocess.cpython-38-darwin.so'\>,'\_signal': \<module '\_signal' (built-**in**)\>,'\_sitebuiltins': \<module '\_sitebuiltins' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/\_sitebuiltins.py'\>,'\_sre': \<module '\_sre' (built-**in**)\>,'\_stat': \<module '\_stat' (built-**in**)\>,'\_thread': \<module '\_thread' (built-**in**)\>,'\_warnings': \<module '\_warnings' (built-**in**)\>,'\_weakref': \<module '\_weakref' (built-**in**)\>,'\_weakrefset': \<module '\_weakrefset' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/\_weakrefset.py'\>,'abc': \<module 'abc' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/abc.py'\>,'ast': \<module 'ast' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/ast.py'\>,'atexit': \<module 'atexit' (built-**in**)\>,'builtins': \<module 'builtins' (built-**in**)\>,'codecs': \<module 'codecs' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/codecs.py'\>,'collections': \<module 'collections' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/collections/\_\_init\_\_.py'\>,'collections.abc': \<module 'collections.abc' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/collections/abc.py'\>,'contextlib': \<module 'contextlib' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/contextlib.py'\>,'copyreg': \<module 'copyreg' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/copyreg.py'\>,'dis': \<module 'dis' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/dis.py'\>,'encodings': \<module 'encodings' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/encodings/\_\_init\_\_.py'\>,'encodings.aliases': \<module 'encodings.aliases' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/encodings/aliases.py'\>,'encodings.latin\_1': \<module 'encodings.latin\_1' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/encodings/latin\_1.py'\>,'encodings.utf\_8': \<module 'encodings.utf\_8' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/encodings/utf\_8.py'\>,'enum': \<module 'enum' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/enum.py'\>,'errno': \<module 'errno' (built-**in**)\>,'functools': \<module 'functools' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/functools.py'\>,'genericpath': \<module 'genericpath' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/genericpath.py'\>,'heapq': \<module 'heapq' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/heapq.py'\>,'importlib': \<module 'importlib' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/importlib/\_\_init\_\_.py'\>,'importlib.\_bootstrap': \<module 'importlib.\_bootstrap' (frozen)\>,'importlib.\_bootstrap\_external': \<module 'importlib.\_bootstrap\_external' (frozen)\>,'importlib.abc': \<module 'importlib.abc' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/importlib/abc.py'\>,'importlib.machinery': \<module 'importlib.machinery' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/importlib/machinery.py'\>,'importlib.util': \<module 'importlib.util' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/importlib/util.py'\>,'inspect': \<module 'inspect' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/inspect.py'\>,'io': \<module 'io' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/io.py'\>,'itertools': \<module 'itertools' (built-**in**)\>,'keyword': \<module 'keyword' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/keyword.py'\>,'linecache': \<module 'linecache' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/linecache.py'\>,'marshal': \<module 'marshal' (built-**in**)\>,'math': \<module 'math' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/lib-dynload/math.cpython-38-darwin.so'\>,'opcode': \<module 'opcode' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/opcode.py'\>,'operator': \<module 'operator' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/operator.py'\>,'os': \<module 'os' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/os.py'\>,'os.path': \<module 'posixpath' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/posixpath.py'\>,'pkgutil': \<module 'pkgutil' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/pkgutil.py'\>,'platform': \<module 'platform' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/platform.py'\>,'posix': \<module 'posix' (built-**in**)\>,'posixpath': \<module 'posixpath' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/posixpath.py'\>,'pprint': \<module 'pprint' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/pprint.py'\>,'pydoc': \<module 'pydoc' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/pydoc.py'\>,'re': \<module 're' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/re.py'\>,'readline': \<module 'readline' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/lib-dynload/readline.cpython-38-darwin.so'\>,'reprlib': \<module 'reprlib' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/reprlib.py'\>,'rlcompleter': \<module 'rlcompleter' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/rlcompleter.py'\>,'select': \<module 'select' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/lib-dynload/select.cpython-38-darwin.so'\>,'selectors': \<module 'selectors' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/selectors.py'\>,'signal': \<module 'signal' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/signal.py'\>,'site': \<module 'site' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site.py'\>,'sre\_compile': \<module 'sre\_compile' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/sre\_compile.py'\>,'sre\_constants': \<module 'sre\_constants' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/sre\_constants.py'\>,'sre\_parse': \<module 'sre\_parse' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/sre\_parse.py'\>,'stat': \<module 'stat' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/stat.py'\>,'subprocess': \<module 'subprocess' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/subprocess.py'\>,'sys': \<module 'sys' (built-**in**)\>,'threading': \<module 'threading' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/threading.py'\>,'time': \<module 'time' (built-**in**)\>,'token': \<module 'token' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/token.py'\>,'tokenize': \<module 'tokenize' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/tokenize.py'\>,'traceback': \<module 'traceback' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/traceback.py'\>,'types': \<module 'types' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/types.py'\>,'urllib': \<module 'urllib' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/urllib/\_\_init\_\_.py'\>,'urllib.parse': \<module 'urllib.parse' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/urllib/parse.py'\>,'warnings': \<module 'warnings' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/warnings.py'\>,'weakref': \<module 'weakref' **from**'/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/weakref.py'\>,'zipimport': \<module 'zipimport' (frozen)\>}

Question 12

Explain * and **

Answer 12

*args and **kwargs is a common idiom for accepting an arbitrary number of arguments to functions:

\>\>\> **def** foo(\*args):...**for** a **in** args:...**print**(a)...\>\>\> foo(1,2,3)123\>\>\> foo(a=1, b=2, c=3) Traceback (most recent call last):File "<stdin>"</stdin>, line 1, **in** \<module\>TypeError: foo() got an unexpected keyword argument 'a'\>\>\>\>\>\> **def** foo(\*\*kwargs):...**for** a **in** kwargs:...**print**(a, kwargs[a])...\>\>\> foo(1,2,3) Traceback (most recent call last):File "<stdin>"</stdin>, line 1, **in** \<module\>TypeError: foo() takes 0 positional arguments but 3 were given \>\>\> foo(a=1, b=2, c=3) a 1 b 2 c 3

Question 13

How do you go to a specific line number in Sublime Text 3?

Answer 13

ctrl-g

Question 14

How can you quickly inspect an object?

Answer 14

\>\>\> **from** django.contrib.auth **import** get\_user\_model \>\>\> **from** pprint **import** pprint \>\>\> User = get\_user\_model()\>\>\> user = User.objects.first()\>\>\> pprint(user.\_\_dict\_\_){'\_state': \<django.db.models.base.ModelState object at 0x10352e5e0\>,'age': None,'date\_joined': datetime.datetime(2020, 2, 8, 17, 38, 42, 384643, tzinfo=\<UTC\>),'email': 'asdf@asdf.com','first\_name': '','id': 1,'is\_active': True,'is\_staff': True,'is\_superuser': True,'last\_login': datetime.datetime(2020, 2, 8, 19, 33, 29, 257231, tzinfo=\<UTC\>),'last\_name': '','password': 'pbkdf2\_sha256$180000$HDGLb5M1aoMb$nCG7eCIlAbVucVwMAsgbxWA5Vgz2P4ihNGF+55r5FDA=','student\_id': None,'username': 'admin'}

Question 15

Write the shortest possible function using any() to test for a palindrome.

Write the shortest possible function using all() to test for a palindrome.

Answer 15

**def** palindromic(sequence):"""Return True if the sequence is the same thing in reverse."""**return** all( n == m **for** n, m **in** zip(sequence, reversed(sequence)))

**def** palindromic(sequence):"""Return True if the sequence is the same thing in reverse."""**return** **not** any( n != m **for** n, m **in** zip(sequence, reversed(sequence)))