Python使用for循环从txt文件读取特定的乘法行

Question

I want use python to read specific multiply lines from txt files. For example ,read line 7 to 10, 17 to 20, 27 to 30 etc.

Here is the code I write, but it will only print out the first 3 lines numbers. Why? I am very new to use Python.

with open('OpenDR Data.txt', 'r') as f:  
    for poseNum in range(0, 4):               
        Data = f.readlines()[7+10*poseNum:10+10*poseNum] 
        for line in Data: 
            matAll = line.split()    
            MatList = map(float, matAll) 
            MatArray1D = np.array(MatList)
            print MatArray1D

Answer 1

with open('OpenDR Data.txt') as f:
    lines = f.readlines()

for poseNum in range(0, 4):               
    Data = lines[7+10*poseNum:10+10*poseNum]

Answer 2

This simplifies the math a little to choose the relevant lines. You don't need to use readlines() .

with open('OpenDR Data.txt', 'r') as fp:
    for idx, line in enumerate(fp, 1):
        if idx % 10 in [7,8,9,0]:
            matAll = line.split()    
            MatList = map(float, matAll) 
            MatArray1D = np.array(MatList)
            print MatArray1D

Answer 3

You should only call readlines() once, so you should do it outside the loop:

with open('OpenDR Data.txt', 'r') as f:  
    lines = f.readlines()
    for poseNum in range(0, 4):               
        Data = lines[7+10*poseNum:10+10*poseNum] 
        for line in Data: 
            matAll = line.split()    
            MatList = map(float, matAll) 
            MatArray1D = np.array(MatList)
            print MatArray1D

Answer 4

You can use a combination list slicing and comprehension.

start = 7
end = 10
interval = 10
groups = 3

with open('data.txt') as f:
    lines = f.readlines()
    mult_lines = [lines[start-1 + interval*i:end + interval*i] for i in range(groups)]

This will return a list of lists containing each group of lines (ie 7 thru 10, 17 thru 20).