27 個為什么，幫助你更好的理解Python

if (x <= y)        x++;        y--;z++;

>>> 1.2 - 1.00.19999999999999996

>>> x = 1.2

1.0011001100110011001100110011001100110011001100110011 (binary)

1.1999999999999999555910790149937383830547332763671875 (decimal)

while True:    line = f.readline()    if not line:        break    ...  # do something with line

if (x = 0) {    // error handling}else {    // code that only works for nonzero x}

line = f.readline()while line:    ...  # do something with line...    line = f.readline()

for line in f:    ...  # do something with line...

"1, 2, 4, 8, 16".split(", ")

try:    value = mydict[key]except KeyError:    mydict[key] = getvalue(key)    value = mydict[key]

if key in mydict:    value = mydict[key]else:    value = mydict[key] = getvalue(key)

def function_1(...):    ...
functions = {'a': function_1,             'b': function_2,             'c': self.method_1, ...}
func = functions[value]func()

def visit_a(self, ...):    ......
def dispatch(self, value):    method_name = 'visit_' + str(value)    method = getattr(self, method_name)    method()

for file in very_long_list_of_files:    f = open(file)    c = f.read(1)

for file in very_long_list_of_files:    with open(file) as f:        c = f.read(1)

class ListWrapper:    def __init__(self, the_list):        self.the_list = the_list
    def __eq__(self, other):        return self.the_list == other.the_list
    def __hash__(self):        l = self.the_list        result = 98767 - len(l)*555        for i, el in enumerate(l):            try:                result = result + (hash(el) % 9999999) * 1001 + i            except Exception:                result = (result % 7777777) + i * 333        return result

for key in sorted(mydict):    ...  # do whatever with mydict[key]...

class label(Exception): pass  # declare a label
try:    ...    if condition: raise label()  # goto label    ...except label:  # where to goto    pass...

f = open("/mydir/file.txt")  # works fine!

dir = r"\this\is\my\dos\dir" "\\"dir = r"\this\is\my\dos\dir\ "[:-1]dir = "\\this\\is\\my\\dos\\dir\\"

with obj:    a = 1               # equivalent to obj.a = 1    total = total + 1   # obj.total = obj.total + 1

def foo(a):    with a:        print(x)

function(args).mydict[index][index].a = 21function(args).mydict[index][index].b = 42function(args).mydict[index][index].c = 63

ref = function(args).mydict[index][index]ref.a = 21ref.b = 42ref.c = 63

if a == b    print(a)

if a == b:    print(a)

[1, 2, 3,]('a', 'b', 'c',)d = {    "A": [1, 5],    "B": [6, 7],  # last trailing comma is optional but good style}

x = [  "fee",  "fie"  "foo",  "fum"]