Here is an analysis of how often certain node types are found in Python (v2.6) ASTs (abstract syntax trees). The data it was collected on consisted of:

Total number of:
    Files:         38106
    Lines of code: 7511158
    AST nodes:     28161457

See also my AST viewer

#node namecountpercentage
1Load712283825.293
2Name624120522.162
3Attribute20415807.250
4Str18069986.417
5Call15695135.573
6Store13417464.764
7Assign10300063.658
8Num8835083.137
9Expr6544942.324
10Param5977082.122
11arguments3413421.212
12BinOp3342101.187
13If3338821.186
14FunctionDef3279931.165
15Subscript3126161.110
16Index2806240.996
17Tuple2800480.994
18Compare2475740.879
19Return2402680.853
20List1943800.690
21keyword1767540.628
22alias1680480.597
23Add1622380.576
24Eq1091620.388
25For853390.303
26Mod837130.297
27Dict821020.292
28ImportFrom676870.240
29UnaryOp622400.221
30BoolOp562860.200
31Import544490.193
32Not543870.193
33ClassDef508490.181
34Mult474530.169
35AugAssign465880.165
36Print408530.145
37Sub404030.143
38Raise382540.136
39Module381060.135
40Slice358140.127
41ExceptHandler350720.125
42And347030.123
43TryExcept334110.119
44In301380.107
45Assert266600.095
46Is245530.087
47NotEq227900.081
48Or215830.077
49comprehension213350.076
50Div206860.073
51ListComp191220.068
52Pass186710.066
53IsNot159970.057
54Gt151330.054
55Lambda133490.047
56Lt132510.047
57While99590.035
58Pow86480.031
59Continue77410.027
60Del75370.027
61Break72620.026
62NotIn72590.026
63Delete70510.025
64USub70140.025
65BitAnd62150.022
66GtE61490.022
67Yield60640.022
68BitOr51940.018
69LtE42400.015
70Global35620.013
71ExtSlice34630.012
72TryFinally33400.012
73LShift21540.008
74GeneratorExp19690.007
75RShift19080.007
76BitXor12410.004
77FloorDiv9450.003
78IfExp5590.002
79Invert5540.002
80Repr5420.002
81Exec4720.002
82With3360.001
83UAdd2850.001
84Ellipsis820.000