Python將相等值解釋為不相等

Question

對於這部分代碼，它位於for循環內

s = 'cl_num = %d, prev_cl_num = %d\n' % (cl_num, prev_cl_num);
fd.write( s );
if cl_num != prev_cl_num:
    bb.instructions[i].is_cache_miss = 1;
    s = 'instruction %x is cache miss, cl_num = %d, prev_cl_num = %d, base_cache_line = %d\n' % (bb.instructions[i].address, cl_num, prev_cl_num, base_cache_line);
    fd.write( s );
    bb.instructions[i].cache_line = cl_num - base_cache_line;
    prev_cl_num = cl_num;

我得到一個輸出，就像在fd文件中一樣，

cl_num = 65557, prev_cl_num = 65557
instruction 400558 is cache miss, cl_num = 65557, prev_cl_num = 65557, base_cache_line = 65557
cl_num = 65557, prev_cl_num = 65557
instruction 400560 is cache miss, cl_num = 65557, prev_cl_num = 65557, base_cache_line = 65557
cl_num = 65557, prev_cl_num = 65557
instruction 400568 is cache miss, cl_num = 65557, prev_cl_num = 65557, base_cache_line = 65557
cl_num = 65557, prev_cl_num = 65557
instruction 400570 is cache miss, cl_num = 65557, prev_cl_num = 65557, base_cache_line = 65557

您會看到，即使cl_num等於prev_cl_num ，條件cl_num != prev_cl_num被評估為true 。 為什么這樣？

Answer 1

您具有浮點值，但僅將整數部分寫入文件：

>>> '%d' % 3.3
'3'

注意.3小數部分如何被忽略； %d對插值調用int() 。

編寫調試值時，請始終在格式中使用repr()或%r ：

s = 'cl_num = %r, prev_cl_num = %r\n' % (cl_num, prev_cl_num);

浮點值的repr()格式化它們就像使用%17g格式化程序一樣； 顯示的是17位小數，當指數為17或更高時，將使用科學計數法。