kangfend · July 1, 2016 12:45 · Jun 27, 2016 · Dec 11, 2015 · Dec 10, 2015 · Oct 2, 2014
diff --git a/beautiful_idiomatic_python.md b/beautiful_idiomatic_python.md
@@ -181,7 +181,7 @@ def find(seq, target):
 
 Inside of every `for` loop is an `else`.
 
-## Looping over dicitonary keys
+## Looping over dictionary keys
 
 ```python
 d = {'matthew': 'blue', 'rachel': 'green', 'raymond': 'red'}
@@ -201,7 +201,7 @@ When should you use the second and not the first? When you're mutating the dicti
 `d.keys()` makes a copy of all the keys and stores them in a list. Then you can modify the dictionary.
 Note: in python 3 to iterate through a dictionary you have to explicidly write: `list(d.keys())` because `d.keys()` returns a "dictionary view" (an iterable that provide a dynamic view on the dictionary’s keys). See [documentation](https://docs.python.org/3/library/stdtypes.html#dict-views).
 
-## Looping over dicitonary keys and values
+## Looping over dictionary keys and values
 
 ```python
 # Not very fast, has to re-hash every key and do a lookup
@@ -509,7 +509,8 @@ names.appendleft('mark')
 
 ```python
 # Mixes business / administrative logic and is not reusable
-def web_lookup(url, saved={}): if url in saved:
+def web_lookup(url, saved={}):
+    if url in saved:
         return saved[url]
     page = urllib.urlopen(url).read()
     saved[url] = page

diff --git a/beautiful_idiomatic_python.md b/beautiful_idiomatic_python.md
@@ -95,7 +95,7 @@ for name, color in izip(names, colors):
 ```
 
 `zip` creates a new list in memory and takes more memory. `izip` is more efficient than `zip`.
-Note: `izip` was renamed to `zip` in python 3.
+Note: in python 3 `izip` was renamed to `zip` and promoted to a builtin replacing the old `zip`.
 
 ## Looping in sorted order
 
@@ -199,7 +199,7 @@ When should you use the second and not the first? When you're mutating the dicti
 > If you mutate something while you're iterating over it, you're living in a state of sin and deserve what ever happens to you.
 
 `d.keys()` makes a copy of all the keys and stores them in a list. Then you can modify the dictionary.
-Note: in python 3 you have to write `list(d.keys())` because `d.keys()` returns a "dictionary view". See [documentation](https://docs.python.org/3/library/stdtypes.html#dict-views).
+Note: in python 3 to iterate through a dictionary you have to explicidly write: `list(d.keys())` because `d.keys()` returns a "dictionary view" (an iterable that provide a dynamic view on the dictionary’s keys). See [documentation](https://docs.python.org/3/library/stdtypes.html#dict-views).
 
 ## Looping over dicitonary keys and values
 
@@ -221,7 +221,7 @@ for k, v in d.iteritems():
 ```
 
 `iteritems()` is better as it returns an iterator.
-Note: in python 3 there is no `iteritems()` and `items()` behaviour is close to what `iteritems()` did. See [documentation](https://docs.python.org/3/library/stdtypes.html#dict-views).
+Note: in python 3 there is no `iteritems()` and `items()` behaviour is close to what `iteritems()` had. See [documentation](https://docs.python.org/3/library/stdtypes.html#dict-views).
 
 ## Construct a dictionary from pairs
 
@@ -524,7 +524,7 @@ def web_lookup(url):
     return urllib.urlopen(url).read()
 ```
 
-Note since python 3.2 there is a decorator for this in the standard library: `functools.lru_cache`.
+Note: since python 3.2 there is a decorator for this in the standard library: `functools.lru_cache`.
 
 ## Factor-out temporary contexts
 

diff --git a/beautiful_idiomatic_python.md b/beautiful_idiomatic_python.md
@@ -20,7 +20,7 @@ for i in range(6):
 for i in xrange(6):
     print i**2
 ```
-`xrange` creates an iterator over the range producing the values one at a time. This approach is much more memory efficient than `range`. `xrange` was renamed `range` in python 3.
+`xrange` creates an iterator over the range producing the values one at a time. This approach is much more memory efficient than `range`. `xrange` was renamed to `range` in python 3.
 
 ## Looping over a collection
 
@@ -95,6 +95,7 @@ for name, color in izip(names, colors):
 ```
 
 `zip` creates a new list in memory and takes more memory. `izip` is more efficient than `zip`.
+Note: `izip` was renamed to `zip` in python 3.
 
 ## Looping in sorted order
 
@@ -198,6 +199,7 @@ When should you use the second and not the first? When you're mutating the dicti
 > If you mutate something while you're iterating over it, you're living in a state of sin and deserve what ever happens to you.
 
 `d.keys()` makes a copy of all the keys and stores them in a list. Then you can modify the dictionary.
+Note: in python 3 you have to write `list(d.keys())` because `d.keys()` returns a "dictionary view". See [documentation](https://docs.python.org/3/library/stdtypes.html#dict-views).
 
 ## Looping over dicitonary keys and values
 
@@ -219,7 +221,8 @@ for k, v in d.iteritems():
 ```
 
 `iteritems()` is better as it returns an iterator.
-
+Note: in python 3 there is no `iteritems()` and `items()` behaviour is close to what `iteritems()` did. See [documentation](https://docs.python.org/3/library/stdtypes.html#dict-views).
+
 ## Construct a dictionary from pairs
 
 ```python
@@ -229,6 +232,7 @@ colors = ['red', 'green', 'blue']
 d = dict(izip(names, colors))
 # {'matthew': 'blue', 'rachel': 'green', 'raymond': 'red'}
 ```
+For python 3: `d = dict(zip(names, colors))`
 
 ## Counting with dictionaries
 
@@ -520,6 +524,8 @@ def web_lookup(url):
     return urllib.urlopen(url).read()
 ```
 
+Note since python 3.2 there is a decorator for this in the standard library: `functools.lru_cache`.
+
 ## Factor-out temporary contexts
 
 ```python
@@ -595,6 +601,7 @@ with ignored(OSError):
 ```
 
 `ignored` is is new in python 3.4, [documentation](http://docs.python.org/dev/library/contextlib.html#contextlib.ignored).
+Note: `ignored` is actually called `suppress` in the standard library.
 
 To make your own `ignored` context manager in the meantime:
 

diff --git a/beautiful_idiomatic_python.md b/beautiful_idiomatic_python.md
@@ -496,10 +496,10 @@ names.popleft()
 names.appendleft('mark')
 ```
 ## Decorators and Context Managers
- * Helps separate business logic from administra:ve logic
- * Clean, beau:ful tools for factoring code and improving code reuse
- * Good naming is essen:al.
- * Remember the Spiderman rule: With great power, comes great respsonsibility!
+ * Helps separate business logic from administrative logic
+ * Clean, beautiful tools for factoring code and improving code reuse
+ * Good naming is essential.
+ * Remember the Spiderman rule: With great power, comes great responsibility!
 
 ## Using decorators to factor-out administrative logic
 

diff --git a/beautiful_idiomatic_python.md b/beautiful_idiomatic_python.md
@@ -645,7 +645,7 @@ def redirect_stdout(fileobj):
         sys.stdout = oldstdout
 ```
 
-# Concise Expressive One-Liners
+## Concise Expressive One-Liners
 Two conflicting rules:
 
  * Don’t put too much on one line

diff --git a/beautiful_idiomatic_python.md b/beautiful_idiomatic_python.md
@@ -0,0 +1,674 @@
+# Transforming Code into Beautiful, Idiomatic Python
+
+Notes from Raymond Hettinger's talk at pycon US 2013 [video](http://www.youtube.com/watch?feature=player_embedded&v=OSGv2VnC0go), [slides](https://speakerdeck.com/pyconslides/transforming-code-into-beautiful-idiomatic-python-by-raymond-hettinger-1).
+
+The code examples and direct quotes are all from Raymond's talk. I've reproduced them here for my own edification and the hopes that others will find them as handy as I have!
+
+## Looping over a range of numbers
+
+```python
+for i in [0, 1, 2, 3, 4, 5]:
+    print i**2
+
+for i in range(6):
+    print i**2
+```
+
+### Better
+
+```python
+for i in xrange(6):
+    print i**2
+```
+`xrange` creates an iterator over the range producing the values one at a time. This approach is much more memory efficient than `range`. `xrange` was renamed `range` in python 3.
+
+## Looping over a collection
+
+```python
+colors = ['red', 'green', 'blue', 'yellow']
+
+for i in range(len(colors)):
+    print colors[i]
+```
+
+### Better
+
+```python
+for color in colors:
+    print color
+```
+
+## Looping backwards
+
+```python
+colors = ['red', 'green', 'blue', 'yellow']
+
+for i in range(len(colors)-1, -1, -1):
+    print colors[i]
+```
+
+### Better
+
+```python
+for color in reversed(colors):
+    print color
+```
+
+## Looping over a collection and indices
+
+```python
+colors = ['red', 'green', 'blue', 'yellow']
+
+for i in range(len(colors)):
+    print i, '--->', colors[i]
+```
+
+### Better
+
+```python
+for i, color in enumerate(colors):
+    print i, '--->', color
+```
+> It's fast and beautiful and saves you from tracking the individual indices and incrementing them.
+
+> Whenever you find yourself manipulating indices [in a collection], you're probably doing it wrong.
+
+## Looping over two collections
+
+```python
+names = ['raymond', 'rachel', 'matthew']
+colors = ['red', 'green', 'blue', 'yellow']
+
+n = min(len(names), len(colors))
+for i in range(n):
+    print names[i], '--->', colors[i]
+
+for name, color in zip(names, colors):
+    print name, '--->', color
+```
+
+### Better
+
+```python
+for name, color in izip(names, colors):
+    print name, '--->', color
+```
+
+`zip` creates a new list in memory and takes more memory. `izip` is more efficient than `zip`.
+
+## Looping in sorted order
+
+```python
+colors = ['red', 'green', 'blue', 'yellow']
+
+# Forward sorted order
+for color in sorted(colors):
+    print colors
+
+# Backwards sorted order
+for color in sorted(colors, reverse=True):
+    print colors
+```
+
+## Custom Sort Order
+
+```python
+colors = ['red', 'green', 'blue', 'yellow']
+
+def compare_length(c1, c2):
+    if len(c1) < len(c2): return -1
+    if len(c1) > len(c2): return 1
+    return 0
+
+print sorted(colors, cmp=compare_length)
+```
+
+### Better
+
+```python
+print sorted(colors, key=len)
+```
+
+The original is slow and unpleasant to write. Also, comparison functions are no longer available in python 3.
+
+## Call a function until a sentinel value
+
+```python
+blocks = []
+while True:
+    block = f.read(32)
+    if block == '':
+        break
+    blocks.append(block)
+```
+
+### Better
+
+```python
+blocks = []
+for block in iter(partial(f.read, 32), ''):
+    blocks.append(block)
+```
+
+`iter` takes two arguments. The first you call over and over again and the second is a sentinel value.
+
+## Distinguishing multiple exit points in loops
+
+```python
+def find(seq, target):
+    found = False
+    for i, value in enumerate(seq):
+        if value == target:
+            found = True
+            break
+    if not found:
+        return -1
+    return i
+```
+
+### Better
+
+```python
+def find(seq, target):
+    for i, value in enumerate(seq):
+        if value == target:
+            break
+    else:
+        return -1
+    return i
+```
+
+Inside of every `for` loop is an `else`.
+
+## Looping over dicitonary keys
+
+```python
+d = {'matthew': 'blue', 'rachel': 'green', 'raymond': 'red'}
+
+for k in d:
+    print k
+
+for k in d.keys():
+    if k.startswith('r'):
+        del d[k]
+```
+
+When should you use the second and not the first? When you're mutating the dictionary.
+
+> If you mutate something while you're iterating over it, you're living in a state of sin and deserve what ever happens to you.
+
+`d.keys()` makes a copy of all the keys and stores them in a list. Then you can modify the dictionary.
+
+## Looping over dicitonary keys and values
+
+```python
+# Not very fast, has to re-hash every key and do a lookup
+for k in d:
+    print k, '--->', d[k]
+
+# Makes a big huge list
+for k, v in d.items():
+    print k, '--->', v
+```
+
+### Better
+
+```python
+for k, v in d.iteritems():
+    print k, '--->', v
+```
+
+`iteritems()` is better as it returns an iterator.
+
+## Construct a dictionary from pairs
+
+```python
+names = ['raymond', 'rachel', 'matthew']
+colors = ['red', 'green', 'blue']
+
+d = dict(izip(names, colors))
+# {'matthew': 'blue', 'rachel': 'green', 'raymond': 'red'}
+```
+
+## Counting with dictionaries
+
+```python
+colors = ['red', 'green', 'red', 'blue', 'green', 'red']
+
+# Simple, basic way to count. A good start for beginners.
+d = {}
+for color in colors:
+    if color not in d:
+        d[color] = 0
+    d[color] += 1
+
+# {'blue': 1, 'green': 2, 'red': 3}
+```
+
+### Better
+
+```python
+d = {}
+for color in colors:
+    d[color] = d.get(color, 0) + 1
+
+# Slightly more modern but has several caveats, better for advanced users
+# who understand the intricacies
+d = defaultdict(int)
+for color in colors:
+d[color] += 1
+```
+
+## Grouping with dictionaries -- Part I and II
+
+```python
+names = ['raymond', 'rachel', 'matthew', 'roger',
+         'betty', 'melissa', 'judith', 'charlie']
+
+# In this example, we're grouping by name length
+d = {}
+for name in names:
+    key = len(name)
+    if key not in d:
+        d[key] = []
+    d[key].append(name)
+
+# {5: ['roger', 'betty'], 6: ['rachel', 'judith'], 7: ['raymond', 'matthew', 'melissa', 'charlie']}
+
+d = {}
+for name in names:
+    key = len(name)
+    d.setdefault(key, []).append(name)
+```
+
+### Better
+
+```python
+d = defaultdict(list)
+for name in names:
+    key = len(name)
+    d[key].append(name)
+```
+
+## Is a dictionary popitem() atomic?
+
+```python
+d = {'matthew': 'blue', 'rachel': 'green', 'raymond': 'red'}
+
+while d:
+    key, value = d.popitem()
+    print key, '-->', value
+```
+
+`popitem` is atomic so you don't have to put locks around it to use it in threads.
+
+## Linking dictionaries
+
+```python
+defaults = {'color': 'red', 'user': 'guest'}
+parser = argparse.ArgumentParser()
+parser.add_argument('-u', '--user')
+parser.add_argument('-c', '--color')
+namespace = parser.parse_args([])
+command_line_args = {k:v for k, v in vars(namespace).items() if v}
+
+# The common approach below allows you to use defaults at first, then override them
+# with environment variables and then finally override them with command line arguments.
+# It copies data like crazy, unfortunately.
+d = defaults.copy()
+d.update(os.environ)
+d.update(command_line_args)
+```
+
+### Better
+
+```python
+d = ChainMap(command_line_args, os.environ, defaults)
+```
+
+`ChainMap` has been introduced into python 3. Fast and beautiful.
+
+## Improving Clarity
+ * Positional arguments and indicies are nice
+ * Keywords and names are better
+ * The first way is convenient for the computer
+ * The second corresponds to how human’s think
+
+## Clarify function calls with keyword arguments
+
+```python
+twitter_search('@obama', False, 20, True)
+```
+
+### Better
+
+```python
+twitter_search('@obama', retweets=False, numtweets=20, popular=True)
+```
+
+Is slightly (microseconds) slower but is worth it for the code clarity and developer time savings.
+
+## Clarify multiple return values with named tuples
+
+```python
+# Old testmod return value
+doctest.testmod()
+# (0, 4)
+# Is this good or bad? You don't know because it's not clear.
+```
+
+### Better
+
+```python
+# New testmod return value, a namedTuple
+doctest.testmod()
+# TestResults(failed=0, attempted=4)
+```
+
+A namedTuple is a subclass of tuple so they still work like a regular tuple, but are more friendly.
+
+To make a namedTuple:
+
+```python
+TestResults = namedTuple('TestResults', ['failed', 'attempted'])
+```
+
+## Unpacking sequences
+
+```python
+p = 'Raymond', 'Hettinger', 0x30, '[email protected]'
+
+# A common approach / habit from other languages
+fname = p[0]
+lname = p[1]
+age = p[2]
+email = p[3]
+```
+
+### Better
+
+```python
+fname, lname, age, email = p
+```
+
+The second approach uses tuple unpacking and is faster and more readable.
+
+## Updating multiple state variables
+
+```python
+def fibonacci(n):
+    x = 0
+    y = 1
+    for i in range(n):
+        print x
+        t = y
+        y = x + y
+        x = t
+```
+
+### Better
+
+```python
+def fibonacci(n):
+    x, y = 0, 1
+    for i in range(n):
+        print x
+        x, y = y, x + y
+```
+
+Problems with first approach
+
+ * x and y are state, and state should be updated all at once or in between lines that state is mis-matched and a common source of issues
+ * ordering matters
+ * it's too low level
+
+
+The second approach is more high-level, doesn't risk getting the order wrong and is fast.
+
+## Simultaneous state updates
+
+```python
+tmp_x = x + dx * t
+tmp_y = y + dy * t
+tmp_dx = influence(m, x, y, dx, dy, partial='x')
+tmp_dy = influence(m, x, y, dx, dy, partial='y')
+x = tmp_x
+y = tmp_y
+dx = tmp_dx
+dy = tmp_dy
+```
+
+### Better
+
+```python
+x, y, dx, dy = (x + dx * t,
+                y + dy * t,
+                influence(m, x, y, dx, dy, partial='x'),
+                influence(m, x, y, dx, dy, partial='y'))
+```
+
+## Efficiency
+ * An optimization fundamental rule
+ * Don’t cause data to move around unnecessarily
+ * It takes only a little care to avoid O(n**2) behavior instead of linear behavior
+
+> Basically, just don't move data around unecessarily.
+
+## Concatenating strings
+
+```python
+names = ['raymond', 'rachel', 'matthew', 'roger',
+         'betty', 'melissa', 'judith', 'charlie']
+
+s = names[0]
+for name in names[1:]:
+    s += ', ' + name
+print s
+```
+
+### Better
+
+```python
+print ', '.join(names)
+```
+
+## Updating sequences
+
+```python
+names = ['raymond', 'rachel', 'matthew', 'roger',
+         'betty', 'melissa', 'judith', 'charlie']
+
+del names[0]
+# The below are signs you're using the wrong data structure
+names.pop(0)
+names.insert(0, 'mark')
+```
+
+### Better
+
+```python
+names = deque(['raymond', 'rachel', 'matthew', 'roger',
+               'betty', 'melissa', 'judith', 'charlie'])
+
+# More efficient with deque
+del names[0]
+names.popleft()
+names.appendleft('mark')
+```
+## Decorators and Context Managers
+ * Helps separate business logic from administra:ve logic
+ * Clean, beau:ful tools for factoring code and improving code reuse
+ * Good naming is essen:al.
+ * Remember the Spiderman rule: With great power, comes great respsonsibility!
+
+## Using decorators to factor-out administrative logic
+
+```python
+# Mixes business / administrative logic and is not reusable
+def web_lookup(url, saved={}): if url in saved:
+        return saved[url]
+    page = urllib.urlopen(url).read()
+    saved[url] = page
+    return page
+```
+
+### Better
+
+```python
+@cache
+def web_lookup(url):
+    return urllib.urlopen(url).read()
+```
+
+## Factor-out temporary contexts
+
+```python
+# Saving the old, restoring the new
+old_context = getcontext().copy()
+getcontext().prec = 50
+print Decimal(355) / Decimal(113)
+setcontext(old_context)
+```
+
+### Better
+
+```python
+with localcontext(Context(prec=50)):
+    print Decimal(355) / Decimal(113)
+```
+
+## How to open and close files
+
+```python
+f = open('data.txt')
+try:
+    data = f.read()
+finally:
+    f.close()
+```
+
+### Better
+
+```python
+with open('data.txt') as f:
+    data = f.read()
+```
+
+## How to use locks
+
+```python
+# Make a lock
+lock = threading.Lock()
+
+# Old-way to use a lock
+lock.acquire()
+try:
+    print 'Critical section 1'
+    print 'Critical section 2'
+finally:
+    lock.release()
+```
+
+### Better
+
+```python
+# New-way to use a lock
+with lock:
+    print 'Critical section 1'
+    print 'Critical section 2'
+```
+
+## Factor-out temporary contexts
+
+```python
+try:
+    os.remove('somefile.tmp')
+except OSError:
+    pass
+```
+
+### Better
+
+```python
+with ignored(OSError):
+    os.remove('somefile.tmp')
+```
+
+`ignored` is is new in python 3.4, [documentation](http://docs.python.org/dev/library/contextlib.html#contextlib.ignored).
+
+To make your own `ignored` context manager in the meantime:
+
+```python
+@contextmanager
+def ignored(*exceptions):
+    try:
+        yield
+    except exceptions:
+        pass
+```
+
+> Stick that in your utils directory and you too can ignore exceptions
+
+## Factor-out temporary contexts
+
+```python
+# Temporarily redirect standard out to a file and then return it to normal
+with open('help.txt', 'w') as f:
+    oldstdout = sys.stdout
+    sys.stdout = f
+    try:
+        help(pow)
+    finally:
+        sys.stdout = oldstdout
+```
+
+### Better
+
+```python
+with open('help.txt', 'w') as f:
+    with redirect_stdout(f):
+        help(pow)
+```
+
+`redirect_stdout` is proposed for python 3.4, [bug report](http://bugs.python.org/issue15805).
+
+To roll your own `redirect_stdout` context manager
+
+```python
+@contextmanager
+def redirect_stdout(fileobj):
+    oldstdout = sys.stdout
+    sys.stdout = fileobj
+    try:
+        yield fieldobj
+    finally:
+        sys.stdout = oldstdout
+```
+
+# Concise Expressive One-Liners
+Two conflicting rules:
+
+ * Don’t put too much on one line
+ * Don’t break atoms of thought into subatomic particles
+
+Raymond’s rule:
+
+ * One logical line of code equals one sentence in English
+
+## List Comprehensions and Generator Expressions
+
+```python
+result = []
+for i in range(10):
+s = i ** 2
+    result.append(s)
+print sum(result)
+```
+
+### Better
+
+```python
+print sum(i**2 for i in xrange(10))
+```
+
+First way tells you what to do, second way tells you what you want.