python open file

1with open("file.txt", "r") as txt_file:
2  return txt_file.readlines()

1# Basic syntax:
2with open('/path/to/filename.extension', 'open_mode') as filename:
3  file_data = filename.readlines()	# Or filename.read() 
4# Where:
5#	- open imports the file as a file object which then needs to be read
6#		with one of the read options
7#	- readlines() imports each line of the file as an element in a list
8#	- read() imports the file contents as one long new-line-separated 
9#		string
10#	- open_mode can be one of:
11#		- "r" = Read which opens a file for reading (error if the file 
12#			doesn't exist)
13#		- "a" = Append which opens a file for appending (creates the 
14#			file if it doesn't exist)
15#		- "w" = Write which opens a file for writing (creates the file 
16#			if it doesn't exist)
17#		- "x" = Create which creates the specified file (returns an error
18#			if the file exists)
19# Note, "with open() as" is recommended because the file is closed 
20#	automatically so you don't have to remember to use file.close()
21
22# Basic syntax for a delimited file with multiple fields:
23import csv
24with open('/path/to/filename.extension', 'open_mode') as filename:
25	file_data = csv.reader(filename, delimiter='delimiter')
26    data_as_list = list(file_data)
27# Where:
28#	- csv.reader can be used for files that use any delimiter, not just
29#		commas, e.g.: '\t', '|', ';', etc. (It's a bit of a misnomer)
30#	- csv.reader() returns a csv.reader object which can be iterated 
31#		over, directly converted to a list, and etc. 
32
33# Importing data using Numpy:
34import numpy as np
35data = np.loadtxt('/path/to/filename.extension',
36				delimiter=',', 	# String used to separate values
37				skiprows=2, 	# Number of rows to skip
38				usecols=[0,2], 	# Specify which columns to read
39				dtype=str) 		# The type of the resulting array
40
41# Importing data using Pandas:
42import pandas as pd
43data = pd.read_csv('/path/to/filename.extension',
44				nrows=5, 		# Number of rows of file to read
45				header=None, 	# Row number to use as column names 
46	            sep='\t', 		# Delimiter to use 
47	            comment='#', 	# Character to split comments
48				na_values=[""])	# String to recognize as NA/NaN
49
50# Note, pandas can also import excel files with pd.read_excel()

1with open('filename', 'a') as f: # able to append data to file
2	f.write(var1) # Were var1 is some variable you have set previously
3	f.write('data') 
4	f.close() # You can add this but it is not mandatory 
5
6with open('filename', 'r') as f: # able to read data from file ( also is the default mode when opening a file in python)
7
8with open('filename', 'x') as f: # Creates new file, if it already exists it will cause it to fail
9
10with open('filename', 't') as f: # opens the file in text mode (also is defualt)
11
12with open('filename', 'b') as f: # Use if your file will contain binary data
13  
14with open('filename', 'w') as f: # Open file with ability to write, will also create the file if it does not exist (if it exists will cause it to fail)
15  
16with open('filename', '+') as f: # Opens file with reading and writing
17
18# You can combine these as you like with the + for reading and writing

1document = 'document.txt'
2file = open(document, 'r')
3# 'r' to read.  it can be replaced with:
4# 'w' to write (overwrite)
5# 'a' to append (add to the end)
6# 'w+' makes a new file if one does not already exist of that name
7# 'a+' same as 'w+' but appends if the file does exist
8# 'x' creates file for writing, but fails if file already exists
9
10##go to beginning of document. not required but good for consistency.
11file.seek(0)
12
13##print all lines in document, except empty lines:
14for line in file:
15    k = line.strip() 
16    print k
17
18##close the file after you are done
19file.close()
20
21
22##this also works to open a file, and is more error proof:
23with open(document) as filestream:
24    for i in filestream:
25        k = i.strip() 
26        print k

1# Reference https://docs.python.org/3/library/functions.html#open
2
3# Method 1
4file = open("welcome.txt", "r") # mode can be r(read) w(write) and others 
5data = file.read()
6file.close()
7
8# Method 2 - automatic close
9with open("welcome.txt") as infile:
10  data = file.read()
11

1def main():
2    f= open("guru99.txt","w+")
3    #f=open("guru99.txt","a+")
4    for i in range(10):
5         f.write("This is line %d\r\n" % (i+1))
6    f.close()
7    #Open the file back and read the contents
8    #f=open("guru99.txt", "r")
9    #if f.mode == 'r':
10    #   contents =f.read()
11    #    print (contents)
12    #or, readlines reads the individual line into a list
13    #fl =f.readlines()
14    #for x in fl:
15    #print(x)
16if __name__== "__main__":
17  main()