一 實戰——讀寫檔案

1 ex16.py

from sys import argv
script, filename = argv
print "We're going to erase %r." % filename
print "If you don't want that, hit CTRL-C (^C)."
print "If you do want that, hit RETURN."
raw_input("?")
print "Opening the file..."
target = open(filename, 'w')
print "Truncating the file. Goodbye!"
target.truncate()
print "Now I'm going to ask you for three lines."
line1 = raw_input("line 1: ")
line2 = raw_input("line 2: ")
line3 = raw_input("line 3: ")
print "I'm going to write these to the file."
target.write(line1)
target.write("\n")
target.write(line2)
target.write("\n")
target.write(line3)
target.write("\n")
print "And finally, we close it."
target.close()
 

2 執行結果

PS E:\Python\exercise> python ex16.py ex16.txt
We're going to erase 'ex16.txt'.
If you don't want that, hit CTRL-C (^C).
If you do want that, hit RETURN.
?
Opening the file...
Truncating the file. Goodbye!
Now I'm going to ask you for three lines.
line 1: yestoday
line 2: today
line 3: tomorrow
I'm going to write these to the file.
And finally, we close it.
 

3 生成檔案內容

yestoday
today
tomorrow

二 實戰——更多檔案操作

1 ex17.py

from sys import argv
from os.path import exists
script, from_file, to_file = argv
print "Copying from %s to %s" % (from_file, to_file)
# we could do these two on one line, how?
in_file = open(from_file)
indata = in_file.read()
print "The input file is %d bytes long" % len(indata)
print "Does the output file exist? %r" % exists(to_file)
print "Ready, hit RETURN to continue, CTRL-C to abort."
raw_input()
out_file = open(to_file, 'w')
out_file.write(indata)
print "Alright, all done."
out_file.close()
in_file.close()
 

2 準備ex16.txt檔案，內容為

yestoday
today
tomorrow

3 執行結果

PS E:\Python\exercise> python ex17.py ex16.txt ex16_new.txt
Copying from ex16.txt to ex16_new.txt
The input file is 24 bytes long
Does the output file exist? False
Ready, hit RETURN to continue, CTRL-C to abort.

Alright, all done.

4 產生檔案ex16_new.txt，檔案內容

yestoday
today
tomorrow

三 實戰——命名, 變數, 程式碼, 函式

1 ex18.py

# this one is like your scripts with argv
def print_two(*args):
    arg1, arg2 = args
    print "arg1: %r, arg2: %r" % (arg1, arg2)
# ok, that *args is actually pointless, we can just do this
def print_two_again(arg1, arg2):
    print "arg1: %r, arg2: %r" % (arg1, arg2)
# this just takes one argument
def print_one(arg1):
    print "arg1: %r" % arg1
# this one takes no arguments
def print_none():
    print "I got nothin'."
print_two("Zed","Shaw")
print_two_again("Zed","Shaw")
print_one("First!")
print_none()

2 執行結果

PS E:\Python\exercise> python ex18.py
arg1: 'Zed', arg2: 'Shaw'
arg1: 'Zed', arg2: 'Shaw'
arg1: 'First!'
I got nothin'.

四 實戰——函式和變數

1 ex19.py

def cheese_and_crackers(cheese_count, boxes_of_crackers):
    print "You have %d cheeses!" % cheese_count
    print "You have %d boxes of crackers!" % boxes_of_crackers
    print "Man that's enough for a party!"
    print "Get a blanket.\n"
    print "We can just give the function numbers directly:"
cheese_and_crackers(20, 30)
print "OR, we can use variables from our script:"
amount_of_cheese = 10
amount_of_crackers = 50
cheese_and_crackers(amount_of_cheese, amount_of_crackers)
print "We can even do math inside too:"
cheese_and_crackers(10 + 20, 5 + 6)
print "And we can combine the two, variables and math:"
cheese_and_crackers(amount_of_cheese + 100, amount_of_crackers + 1000)

2 執行結果

PS E:\Python\exercise> python ex19.py
You have 20 cheeses!
You have 30 boxes of crackers!
Man that's enough for a party!
Get a blanket.

We can just give the function numbers directly:
OR, we can use variables from our script:
You have 10 cheeses!
You have 50 boxes of crackers!
Man that's enough for a party!
Get a blanket.

We can just give the function numbers directly:
We can even do math inside too:
You have 30 cheeses!
You have 11 boxes of crackers!
Man that's enough for a party!
Get a blanket.

We can just give the function numbers directly:
And we can combine the two, variables and math:
You have 110 cheeses!
You have 1050 boxes of crackers!
Man that's enough for a party!
Get a blanket.

五 實戰——函式和檔案

1 ex20.py

from sys import argv
script, input_file = argv
def print_all(f):
    print f.read()
def rewind(f):
    f.seek(0)
def print_a_line(line_count, f):
    print line_count, f.readline()
current_file = open(input_file)
print "First let's print the whole file:\n"
print_all(current_file)
print "Now let's rewind, kind of like a tape."
rewind(current_file)
print "Let's print three lines:"
current_line = 1
print_a_line(current_line, current_file)
current_line = current_line + 1
print_a_line(current_line, current_file)
current_line = current_line + 1
print_a_line(current_line, current_file)

2 準備測試檔案ex16.txt

yestoday
today
tomorrow

3 執行結果

PS E:\Python\exercise> python ex20.py ex16.txt
First let's print the whole file:

yestoday
today
tomorrow

Now let's rewind, kind of like a tape.
Let's print three lines:
1 yestoday

2 today

3 tomorrow