函數只返回最後一項

Question

爲什麼在下面的函數中只返回最後一項呢？

def lem(file): 
    lem = '' 
    for line in file: 
     lem = line.split()[1] 
    return lem 

print(lem(file)) 

Answer 1

因爲您只返回了一件東西（lem正在被重新創建）。如果你想返回不止一兩件事，無論是在連接字符串，返回一個列表，或使它成爲一個generator function：

# Concatenating 
def lem(file): 
    lem = [] 
    for line in file: 
     lem.append(line.split()[1]) 
    return ''.join(lem) 
    # Returning a list is the same, just omit the ''.join() 
# To use when using ''.join, just print the return value 
print(lem(file)) 
# To use when returning a list, loop (as in the generator case below), or print the list itself as in the ''.join case and it will print the list's repr 

# Generator 
def lem(file): 
    for line in file: 
     yield line.split()[1] 
# To use the generator, either loop and print: 
for x in lem(file): 
    print(x) 
# Or splat the result generator to print if you're using Py3's print 
# function (or using from __future__ import print_function on Py2) 
print(*lem(file)) # Separates outputs with spaces; sep="\n" to put them on separate lines, sep="" to print them back-to-back, etc. 
# Or to print (or assign) them all at once as a single string: 
print(''.join(lem(file))) # Change '' to whatever string you want to put between all the outputs 

在發電機的情況下，你需要循環輸出（隱含在潑濺與*或與''.join合併，或明確與for循環），打印直接返回的發電機幾乎是無用的（它將是通用generator的repr，如<generator object lem at 0xdeadbeef>）。

Answer 2

在每次迭代中，您將重新指定lem的值。 您需要在每次迭代之前將其保存爲列表（例如）。

def lem(myfile): 
    res = [] 
    for line in myfile: 
     res.append(line.split()[1]) 
    return ' '.join(res) # joining to string 

print(lem(myfile)) 

並停止使用內置名稱，如file。