python处理写入数据代码讲解

3.1415926535
8979323846
2643383279
with open('pi_digits.txt') as f: # 默认模式为‘r'，只读模式
  contents = f.read() # 读取文件全部内容
  print contents # 输出时在最后会多出一行（read()函数到达文件末会返回一个空字符，显示出空字符就是一个空行）
  print '------------'
  print contents.rstrip() # rstrip()函数用于删除字符串末的空白
3.1415926535
8979323846
2643383279

------------
3.1415926535
8979323846
2643383279

with open('pi_digits.txt') as f:  
for line1 in f:    
print line1 # 每行末尾会有一个换行符
print '------------'
for line2 in f:    
print line2.rstrip() # 此时文件已经读完，line2指向文本末尾，因此不会有输出
3.1415926535

8979323846

2643383279

----------

with open('pi_digits.txt') as f:  
for line1 in f:   
print line1  
print '------------'
with open('pi_digits.txt') as f: # 需要重新打开文本进行读取
for line2 in f:    
print line2.rstrip() # 删除字符串末尾的空白
3.1415926535

8979323846

2643383279

------------
3.1415926535
8979323846
2643383279

with open('pi_digits.txt') as f: 
lines = f.readlines() # 读取文本中所有内容，并保存在一个列表中，列表中每一个元素对应一行数据
print lines # 每一行数据都包含了换行符
print '------------'
for line in lines:  
print line.rstrip()  
print '------------'
pi_str = '' # 初始化为空字符
for line in lines:
pi_str += line.rstrip() #字符串连接
print pi_str
['3.1415926535\n', '8979323846\n', '2643383279\n']
------------
3.1415926535
8979323846
2643383279
------------
3.141592653589793238462643383279

filename = 'write_data.txt'
with open(filename,'w') as f: # 如果filename不存在会自动创建， 'w'表示写数据，写之前会清空文件中的原有数据！
f.write("I am Meringue.\n")
f.write("I am now studying in NJTECH.\n")

I am Meringue.
I am now studying in NJTECH.

with open(filename,'a') as f: # 'a'表示append,即在原来文件内容后继续写数据（不清楚原有数据）
f.write("I major in Machine learning and Computer vision.\n")

I am Meringue.
I am now studying in NJTECH.
I major in Machine learning and Computer vision.