一、int的范围
python2：
在32位机器上，整数的位数为32位，取值范围为-2**31～2**31-1；在64位系统上，整数的位数为64位，取值范围为-2**63～2**63-1；
python3：
理论上长度是无限的（只要内存足够大）
二、python内存机制
在一般情况下当变量被赋值后，内存和变量的关系如下：
特殊情况：
python内的优化机制（不论是2.7还是3.5都有）：
-5 ~ 257 之间的数，如果使用第一种赋值方式，那么他们依然属于同一块内存（可以用id查看）
三、源码
1 class int(object):int
2 """
3 int(x=0) -> int or long
4 int(x, base=10) -> int or long
5
6 Convert a number or string to an integer, or return 0 if no arguments
7 are given. If x is floating point, the conversion truncates towards zero.
8 If x is outside the integer range, the function returns a long instead.
9
10 If x is not a number or if base is given, then x must be a string or
11 Unicode object representing an integer literal in the given base. The
12 literal can be preceded by '+' or '-' and be surrounded by whitespace.
13 The base defaults to 10. Valid bases are 0 and 2-36. Base 0 means to
14 interpret the base from the string as an integer literal.
15 >>> int('0b100', base=0)
16 """
17 def bit_length(self):
18 """ 返回表示该数字的时占用的最少位数 """
19 """
20 int.bit_length() -> int
21
22 Number of bits necessary to represent self in binary.
23 >>> bin(37)
24 '0b100101'
25 >>> (37).bit_length()
26 """
27 return 0
28
29 def conjugate(self, *args, **kwargs): # real signature unknown
30 """ 返回该复数的共轭复数 """
31 """ Returns self, the complex conjugate of any int. """
32 pass
33
34 def __abs__(self):
35 """ 返回绝对值 """
36 """ x.__abs__() <==> abs(x) """
37 pass
38
39 def __add__(self, y):
40 """ x.__add__(y) <==> x+y """
41 pass
42
43 def __and__(self, y):
44 """ x.__and__(y) <==> x&y """
45 pass
46
47 def __cmp__(self, y):
48 """ 比较两个数大小 """
49 """ x.__cmp__(y) <==> cmp(x,y) """
50 pass
51
52 def __coerce__(self, y):
53 """ 强制生成一个元组 """
54 """ x.__coerce__(y) <==> coerce(x, y) """
55 pass
56
57 def __divmod__(self, y):
58 """ 相除，得到商和余数组成的元组 """
59 """ x.__divmod__(y) <==> divmod(x, y) """
60 pass
61
62 def __div__(self, y):
63 """ x.__div__(y) <==> x/y """
64 pass
65
66 def __float__(self):
67 """ 转换为浮点类型 """
68 """ x.__float__() <==> float(x) """
69 pass
70
71 def __floordiv__(self, y):
72 """ x.__floordiv__(y) <==> x//y """
73 pass
74
75 def __format__(self, *args, **kwargs): # real signature unknown
76 pass
77
78 def __getattribute__(self, name):
79 """ x.__getattribute__('name') <==> x.name """
80 pass
81
82 def __getnewargs__(self, *args, **kwargs): # real signature unknown
83 """ 内部调用 __new__方法或创建对象时传入参数使用 """
84 pass
85
86 def __hash__(self):
87 """如果对象object为哈希表类型，返回对象object的哈希值。哈希值为整数。在字典查找中，哈希值用于快速比较字典的键。两个数值如果相等，则哈希值也相等。"""
88 """ x.__hash__() <==> hash(x) """
89 pass
90
91 def __hex__(self):
92 """ 返回当前数的 十六进制 表示 """
93 """ x.__hex__() <==> hex(x) """
94 pass
95
96 def __index__(self):
97 """ 用于切片，数字无意义 """
98 """ x[y:z] <==> x[y.__index__():z.__index__()] """
99 pass
100
101 def __init__(self, x, base=10): # known special case of int.__init__
102 """ 构造方法，执行 x = 123 或 x = int(10) 时，自动调用，暂时忽略 """
103 """
104 int(x=0) -> int or long
105 int(x, base=10) -> int or long
106
107 Convert a number or string to an integer, or return 0 if no arguments
108 are given. If x is floating point, the conversion truncates towards zero.
109 If x is outside the integer range, the function returns a long instead.
110
111 If x is not a number or if base is given, then x must be a string or
112 Unicode object representing an integer literal in the given base. The
113 literal can be preceded by '+' or '-' and be surrounded by whitespace.
114 The base defaults to 10. Valid bases are 0 and 2-36. Base 0 means to
115 interpret the base from the string as an integer literal.
116 >>> int('0b100', base=0)
117 # (copied from class doc)
118 """
119 pass
120
121 def __int__(self):
122 """ 转换为整数 """
123 """ x.__int__() <==> int(x) """
124 pass
125
126 def __invert__(self):
127 """ x.__invert__() <==> ~x """
128 pass
129
130 def __long__(self):
131 """ 转换为长整数 """
132 """ x.__long__() <==> long(x) """
133 pass
134
135 def __lshift__(self, y):
136 """ x.__lshift__(y) <==> x<<y """
137 pass
138
139 def __mod__(self, y):
140 """ x.__mod__(y) <==> x%y """
141 pass
142
143 def __mul__(self, y):
144 """ x.__mul__(y) <==> x*y """
145 pass
146
147 def __neg__(self):
148 """ x.__neg__() <==> -x """
149 pass
150
151 @staticmethod # known case of __new__
152 def __new__(S, *more):
153 """ T.__new__(S, ...) -> a new object with type S, a subtype of T """
154 pass
155
156 def __nonzero__(self):
157 """ x.__nonzero__() <==> x != 0 """
158 pass
159
160 def __oct__(self):
161 """ 返回改值的 八进制 表示 """
162 """ x.__oct__() <==> oct(x) """
163 pass
164
165 def __or__(self, y):
166 """ x.__or__(y) <==> x|y """
167 pass
168
169 def __pos__(self):
170 """ x.__pos__() <==> +x """
171 pass
172
173 def __pow__(self, y, z=None):
174 """ 幂，次方 """
175 """ x.__pow__(y[, z]) <==> pow(x, y[, z]) """
176 pass
177
178 def __radd__(self, y):
179 """ x.__radd__(y) <==> y+x """
180 pass
181
182 def __rand__(self, y):
183 """ x.__rand__(y) <==> y&x """
184 pass
185
186 def __rdivmod__(self, y):
187 """ x.__rdivmod__(y) <==> divmod(y, x) """
188 pass
189
190 def __rdiv__(self, y):
191 """ x.__rdiv__(y) <==> y/x """
192 pass
193
194 def __repr__(self):
195 """转化为解释器可读取的形式 """
196 """ x.__repr__() <==> repr(x) """
197 pass
198
199 def __str__(self):
200 """转换为人阅读的形式，如果没有适于人阅读的解释形式的话，则返回解释器课阅读的形式"""
201 """ x.__str__() <==> str(x) """
202 pass
203
204 def __rfloordiv__(self, y):
205 """ x.__rfloordiv__(y) <==> y//x """
206 pass
207
208 def __rlshift__(self, y):
209 """ x.__rlshift__(y) <==> y<<x """
210 pass
211
212 def __rmod__(self, y):
213 """ x.__rmod__(y) <==> y%x """
214 pass
215
216 def __rmul__(self, y):
217 """ x.__rmul__(y) <==> y*x """
218 pass
219
220 def __ror__(self, y):
221 """ x.__ror__(y) <==> y|x """
222 pass
223
224 def __rpow__(self, x, z=None):
225 """ y.__rpow__(x[, z]) <==> pow(x, y[, z]) """
226 pass
227
228 def __rrshift__(self, y):
229 """ x.__rrshift__(y) <==> y>>x """
230 pass
231
232 def __rshift__(self, y):
233 """ x.__rshift__(y) <==> x>>y """
234 pass
235
236 def __rsub__(self, y):
237 """ x.__rsub__(y) <==> y-x """
238 pass
239
240 def __rtruediv__(self, y):
241 """ x.__rtruediv__(y) <==> y/x """
242 pass
243
244 def __rxor__(self, y):
245 """ x.__rxor__(y) <==> y^x """
246 pass
247
248 def __sub__(self, y):
249 """ x.__sub__(y) <==> x-y """
250 pass
251
252 def __truediv__(self, y):
253 """ x.__truediv__(y) <==> x/y """
254 pass
255
256 def __trunc__(self, *args, **kwargs):
257 """ 返回数值被截取为整形的值，在整形中无意义 """
258 pass
259
260 def __xor__(self, y):
261 """ x.__xor__(y) <==> x^y """
262 pass
263
264 denominator = property(lambda self: object(), lambda self, v: None, lambda self: None) # default
265 """ 分母 = 1 """
266 """the denominator of a rational number in lowest terms"""
267
268 imag = property(lambda self: object(), lambda self, v: None, lambda self: None) # default
269 """ 虚数，无意义 """
270 """the imaginary part of a complex number"""
271
272 numerator = property(lambda self: object(), lambda self, v: None, lambda self: None) # default
273 """ 分子 = 数字大小 """
274 """the numerator of a rational number in lowest terms"""
275
276 real = property(lambda self: object(), lambda self, v: None, lambda self: None) # default
277 """ 实属，无意义 """
278 """the real part of a complex number"""
279
280 int
小知识点：
在python2中：
test = 9 / 2
输出—— 4
from __future__ import division
test = 9 / 2
输出—— 4.5
而在python3中：
test = 9 / 2
输出—— 4.5