如何在Python中打印“美观”的字符串输出

Question

我有一个字典列表，这些字典里有一些字段，比如 classid（课程ID）、dept（系别）、coursenum（课程编号）、area（区域）和 title（标题），这些数据是从 SQL 查询中得到的。我想把这些值以人类易读的格式输出。我在想，能不能在每一列的顶部加上列标题，然后在每一列下面显示相应的内容，比如：

CLASSID     DEPT     COURSE NUMBER        AREA     TITLE
foo         bar      foo                  bar      foo
yoo         hat      yoo                  bar      hat

（当然要保持标准的对齐和间距）

我该怎么在 Python 中实现这个呢？

Answer 1

如果你想让字符串简单一点，可以把它左对齐到一定的字符数：

print string1.ljust(20) + string2.ljust(20)

Answer 2

class TablePrinter(object):
    "Print a list of dicts as a table"
    def __init__(self, fmt, sep=' ', ul=None):
        """        
        @param fmt: list of tuple(heading, key, width)
                        heading: str, column label
                        key: dictionary key to value to print
                        width: int, column width in chars
        @param sep: string, separation between columns
        @param ul: string, character to underline column label, or None for no underlining
        """
        super(TablePrinter,self).__init__()
        self.fmt   = str(sep).join('{lb}{0}:{1}{rb}'.format(key, width, lb='{', rb='}') for heading,key,width in fmt)
        self.head  = {key:heading for heading,key,width in fmt}
        self.ul    = {key:str(ul)*width for heading,key,width in fmt} if ul else None
        self.width = {key:width for heading,key,width in fmt}

    def row(self, data):
        return self.fmt.format(**{ k:str(data.get(k,''))[:w] for k,w in self.width.iteritems() })

    def __call__(self, dataList):
        _r = self.row
        res = [_r(data) for data in dataList]
        res.insert(0, _r(self.head))
        if self.ul:
            res.insert(1, _r(self.ul))
        return '\n'.join(res)

并且在使用中：

data = [
    {'classid':'foo', 'dept':'bar', 'coursenum':'foo', 'area':'bar', 'title':'foo'},
    {'classid':'yoo', 'dept':'hat', 'coursenum':'yoo', 'area':'bar', 'title':'hat'},
    {'classid':'yoo'*9, 'dept':'hat'*9, 'coursenum':'yoo'*9, 'area':'bar'*9, 'title':'hathat'*9}
]

fmt = [
    ('ClassID',       'classid',   11),
    ('Dept',          'dept',       8),
    ('Course Number', 'coursenum', 20),
    ('Area',          'area',       8),
    ('Title',         'title',     30)
]

print( TablePrinter(fmt, ul='=')(data) )

产生了

ClassID     Dept     Course Number        Area     Title                         
=========== ======== ==================== ======== ==============================
foo         bar      foo                  bar      foo                           
yoo         hat      yoo                  bar      hat                           
yooyooyooyo hathatha yooyooyooyooyooyooyo barbarba hathathathathathathathathathat

Answer 3

你可以看看标准的Python字符串格式化，这可能就够用了。

# assume that your data rows are tuples
template = "{0:8}|{1:10}|{2:15}|{3:7}|{4:10}" # column widths: 8, 10, 15, 7, 10
print template.format("CLASSID", "DEPT", "COURSE NUMBER", "AREA", "TITLE") # header
for rec in your_data_source: 
  print template.format(*rec)

或者

# assume that your data rows are dicts
template = "{CLASSID:8}|{DEPT:10}|{C_NUM:15}|{AREA:7}|{TITLE:10}" # same, but named
print template.format( # header
  CLASSID="CLASSID", DEPT="DEPT", C_NUM="COURSE NUMBER", 
  AREA="AREA", TITLE="TITLE"
) 
for rec in your_data_source: 
  print template.format(**rec)

可以尝试调整对齐方式、填充和具体的格式说明符，以获得最佳效果。