在python中读取文件并返回字符串

我的目标是读入一个文件，并返回用户要求的相应信息。例如，我的文本文件如下所示（它表示该年以及该年的学生身高）：

2013年

5.5.6.3 4.0 5.2 5.1

2014年

4.6 4.8 5.3 5.6 6.0

2015年

3.8 4.9 6.0 5.8 5.7

基本上，如果我进入2013年，我希望它返回对应于该年的高度列表（下面的行）。但我无法让它打印回字符串列表。帮点忙就好了

#read in text file
f = open("students.txt")
#ask for student year
year = input("Enter the year for the data you want to receive:")
#check to see if year is avialble
line = f.readline()
while True:
    line = f.readline().split()
    if line:
        if line == year:
            print(line)
    else:
        break
        print("No data")

---

如果执行

f.readline（）.split（）

，则会得到一个列表。因此，对于第一行，您将有类似于

line=['2013']

的内容。另一方面，年份是一根弦。因此，如果用户输入

2013

，

类型（年份）=

，而

类型（行）=

。因为它们永远不相等，所以if子句永远不

True

，并且该行永远不会被打印出来

#read in text file
f = open("students.txt")
#ask for student year
year = input("Enter the year for the data you want to receive:")
#check to see if year is available
for line in f.readlines():
    if year in line:
        f.readline()
        print ( f.readline() )
        break

---

我想，如果有一个身高超过2000的学生，上面的代码就不起作用了。

相反，试着把所有条目都读入字典。那么按年查询就很简单了

def readentries(f):    
    # read until we get `StopException` i.e. end of file
    while True:
        try:
            # take two lines from the file and strip newlines
            # and split heights by spaces to give a list of heights
            yield next(f).strip(), next(f).strip().split()
        except StopIteration:
            # break out of the infinite while loop
            break

with open('heights.txt') as f:
     entries = dict(readentries(f))

year = input("Enter the year for the data you want to receive: ")

# query dict for supplied entry
if year in entries:
    print('for year %s we have heights %s ' % (year, ', '.join(entries[year])))
else:
    print('no data')

---

您可能需要将高度转换为

float

变量。这很容易添加。

一种简单的方法是将文件的所有行读取到列表中，然后根据您想要的年份在该列表中查找索引，然后获取下一行

with open('students.txt', 'r') as f:
    data = [i.strip() for i in f]   # strip trailing space

year = input("Enter year: ")
try:
    # find index, get the next line
    line = data[data.index(year) + 1] 
    # split on whitespace, apply float()
    item_list = [float(i) for i in line.split()]
except ValueError:  # raised if year not found
    print("No relevant data")

---

在与所需年份相等的行后打印下一行而不是空行

year = "2013"

with open("students.txt") as f:
    stop = False
    for line in f:
        line = line.rstrip("\n")
        if line == year:
            stop = True
        else:
            if line and stop:
                print line.split()
                break

    if not stop:
        print "No data for year {}.".format(year)

---

您还可以构建两个列表，并通过迭代文件的行来构建字典：

with open("grade.txt", "r") as file:
    year = []
    height = []
    for i in file:
        if len(i.strip("\n")) == 4:
            year.append(i.strip("\n"))
        elif i != "\n":
            height.append(i.strip("\n").split(" "))
    ydict = {year[i]: height[i] for i in range(len(year))}

print(ydict['2013'])

---

由于数据包含一些空白行和制表符，因此您需要首先清理这些数据。然后，只需将偶数行（年份）添加为字典中的键（从零开始），将奇数行（高度）添加为字典中的值

year = input("Enter the year for the data you want to receive:")
with open("students.txt") as f:
    # read stripped file lines into list keeping only those that contain data
    data = [line.strip() for line in f.readlines() if line.strip() != '']
# build a dict from the data using list slicing to get the years (keys) and heights (values)
data_dict = dict(zip(data[0::2], data[1::2]))
# print the heights if the year exists otherwise 'No data.'
print(data_dict.get(str(year)) if data_dict.get(str(year)) else 'No data.')