如何在Python中读取数组的第一行

Question

我刚开始学习Python，下面是我当前的代码：

#!/usr/bin/python

l = []
with open('datad.dat', 'r') as f:
  for line in f:
    line = line.strip()
    if len(line) > 0:
      l.append(map(float, line.split()))
print l[:,1]

我试图这样做，但犯了使用FORTRAN语法的错误，并收到以下错误：

  File "r1.py", line 9, in <module>
print l[:,1]

类型错误：列表索引必须是整数，而不是元组

如何获取数组的第一行或第一列？

Answer 1

若要打印第一行，请使用l[0]，若要获取列，则需要使用zip print(list(zip(*l))[0])进行转置。

In [14]: l = [[1,2,3],[4,5,6],[7,8,9]]  
In [15]: l[0] # first row
Out[15]: [1, 2, 3]    
In [16]: l[1] # second row
Out[16]: [4, 5, 6]   
In [17]: l[2] # third row
Out[17]: [7, 8, 9]    
In [18]: t =  list(zip(*l)) 
In [19]  t[0] # first column
Out[19]: (1, 4, 7)    
In [20]: t[1] # second column
Out20]: (2, 5, 8)   
In [21]: t[2] # third column
Out[21]: (3, 6, 9)

csv module也可能有用：

import csv

with open('datad.dat', 'r') as f:
   reader = csv.reader(f)
   l = [map(float, row) for row  in reader]