逐行打印第 n 行

Question

我正在尝试打印文件中特定行之后的第 n 行：

import glob
import numpy as np
import matplotlib.pyplot as plt
import math

velerror = []
divergence = []
mesh = []
timestep = []
totaltime = []

for files in glob.glob('*.out'):
    f = open(files, 'r')
    for line in f:
        if "Maximum Velocity Error:" in line:
            velerror.append(float(line[32:40]))
        if "Grid Dimensions, Mesh" in line:
            mesh.append(int(line[27]))
        if "Time Step  " in line:
            timestep.append(int(line[17:27].strip()))
        if "Total time:" in line:
            totaltime.append(float(line[47:57].strip()))
            #Print nth line after line


totaltime = totaltime[0::9]

print(velerror)
print(mesh)
print(timestep)
print(totaltime)

是否有像 next() 这样的函数可以转到下第 n 行？

Answer 1

使用readlines()

i = 0;
lines = f.readlines()
while 1:
    line = lines[i]
    if not line:
        break
    if "Maximum Velocity Error:" in line:
            velerror.append(float(line[32:40]))
    if "Grid Dimensions, Mesh" in line:
            mesh.append(int(line[27]))
    if "Time Step  " in line:
            timestep.append(int(line[17:27].strip()))
    if "Total time:" in line:
            totaltime.append(float(line[47:57].strip()))
            i = i + 8
    i++

Answer 2

（请参阅没有 readlines、live demo 的版本的编辑）

print the nth line after a specific line in a file

如果文件适合内存使用 readlines 和切片：

def print_after(source, specific_line_number, skip_lines):
    for line in source[specific_line_number::skip_lines]:
        print(line)

lines = [f'line {i:2}' for i in range(30)] # readlines here
print_after(lines, 7, 2)

在您的代码中：

import glob
import numpy as np
import matplotlib.pyplot as plt
import math

velerror = []
divergence = []
mesh = []
timestep = []
totaltime = []

for files in glob.glob('*.out'):
    f = open(files, 'r')
    for line in f:
        if "Maximum Velocity Error:" in line:
            velerror.append(float(line[32:40]))
        if "Grid Dimensions, Mesh" in line:
            mesh.append(int(line[27]))
        if "Time Step  " in line:
            timestep.append(int(line[17:27].strip()))
        if "Total time:" in line:
            totaltime.append(float(line[47:57].strip()))
            for line in islice
            break  # Stop consuming lines (?)


totaltime = totaltime[0::9]

print(velerror)
print(mesh)
print(timestep)
print(totaltime)

编辑：按照 rassahah 的建议使用 islice 可以帮助您节省一些内存：

from itertools import islice

import glob
import numpy as np
import matplotlib.pyplot as plt
import math

velerror = []
divergence = []
mesh = []
timestep = []
totaltime = []

for files in glob.glob('*.out'):
    f = open(files, 'r')
    for line in f:
        if "Maximum Velocity Error:" in line:
            velerror.append(float(line[32:40]))
        if "Grid Dimensions, Mesh" in line:
            mesh.append(int(line[27]))
        if "Time Step  " in line:
            timestep.append(int(line[17:27].strip()))
        if "Total time:" in line:
            totaltime.append(float(line[47:57].strip()))
            break
    skip_lines = 2
    offset = skip_lines-1
    for line in islice(f, offset, None, skip_lines):
        print(line)


totaltime = totaltime[0::9]

print(velerror)
print(mesh)
print(timestep)
print(totaltime)

Answer 3

打印每个文件的第 n 行

import glob
import numpy as np
import matplotlib.pyplot as plt
import math

velerror = []
divergence = []
mesh = []
timestep = []
totaltime = []
n_check = 5    # let n be 5

for files in glob.glob('*.out'):
    f = open(files, 'r')
    for i,line in enumerate(f):
        if "Maximum Velocity Error:" in line:
            velerror.append(float(line[32:40]))
        if "Grid Dimensions, Mesh" in line:
            mesh.append(int(line[27]))
        if "Time Step  " in line:
            timestep.append(int(line[17:27].strip()))
        if "Total time:" in line:
            totaltime.append(float(line[47:57].strip()))
        if not i%n_check:
            print(line)

Answer 4

您可以使用关键字搜索特定行并打印第二个关键字的第n行。代码如下

search=open("test.txt",'r') 
for line in search:
   if "first_keyword" in line:
      while not "second_keywoed" in line:
          line=next(search)
      if "second_keyword" in line:
          print(line)

Answer 5

你可以为此使用 linecache 模块

import linecache

line_count = 0
n_lines = 4  # just an example

for file in glob.glob('*.out'):
    with open(file, 'r') as f:
        for line in f:
            line_count += 1
            if "Maximum Velocity Error:" in line:
                velerror.append(float(line[32:40]))
            if "Grid Dimensions, Mesh" in line:
                mesh.append(int(line[27]))
            if "Time Step  " in line:
                timestep.append(int(line[17:27].strip()))
            if "Total time:" in line:
                totaltime.append(float(line[47:57].strip()))
                interesting_line = linecache.getline(file, line_count + n_lines)
                print(interesting_line)

Answer 6

Is there a function like next() that goes to the next nth line?

有一个函数 next() 可以传递当前行并转到下一行。在包 itertools 中有一个函数 islice()，它构建了一个可迭代的子范围（即 next() 继续工作）。幸运的是，文件句柄（从 open() 调用中获得的 f ）也是一个可迭代的，因此您可以将这三个部分组合起来：

from itertools import islice
...
if "Total time:" in line:
  totaltime.append(float(line[47:57].strip()))
  #Print nth line after line
  # Skips to the 5th line, and stops and the 6th line;
  # counting begins at 0, so by human standards this
  # actually prints the 6th line:
  next_5th_line = next (islice (f, 5, 6))
  print (next_5th_line)

执行后，循环将在打印出的行之后继续，因此一些行将被简单地丢弃。

逐行打印第 n 行

Print nth line after line

python

iterable