Basic

Programming_Python

Ver

Basic

7/16/24

Index

Strings

https://www.tutorialspoint.com/python/python_strings.htm

Basic

dotnetperls

String Formatting Operator

One of Python's coolest features is the string format operator %.

other

This operator is unique to strings and makes up for the lack of having functions from C's printf() family.

pip

#!/usr/bin/python3

PySerial

print ("My name is %s and weight

>>>>

My name is Zara and weight is 21 kg!

Format

S.No.

Symbol

Conversion

S.No.

Symbol

Functionality

character

argument specifies width or precision

string conversion via str() prior to formatting

left justification

signed decimal integer

display the sign

signed decimal integer

<sp>

leave a blank space before a positive number

unsigned decimal integer

add the octal leading zero ( '0' ) or hexadecimal leading '0x' or '0X', depending on whether 'x' or 'X' were used.

octal integer

pad from left with zeros (instead of spaces)

hexadecimal integer (lowercase letters)

'%%' leaves you with a single literal '%'

hexadecimal integer (UPPERcase letters)

(var)

mapping variable (dictionary arguments)

exponential notation (with lowercase 'e')

m.n.

m is the minimum total width and n is the number of digits to display after the decimal point (if appl.)

exponential notation (with UPPERcase 'E')

floating point real number

the shorter of %f and %e

the shorter of %f and %E

Strings

Date and Time

https://www.tutorialspoint.com/python/python_date_time.htm

Tick

Time intervals are floating-point numbers in units of seconds

Particular instants in time are expressed in seconds since 12:00am, January 1, 1970(epoch).

There is a popular time module available in Python which provides functions for working with times, and for converting between representations.

The function time.time() returns the current system time in ticks since 12:00am, January 1, 1970(epoch).

Example

Output

#!/usr/bin/python

import time; # This is required to include time module.

ticks = time.time()

print "Number of ticks since 12:00am, January 1, 1970:", ticks

Number of ticks since 12:00am, January 1, 1970: 7186862.73399

TimeTuple

>>>>>>>

This tuple is equivalent to struct_time structure. This structure has the following attributes --

Index

Field

Values

Index

Attribute

Values

4-digit year

2008

tm_year

2008

Month

1 to 12

tm_mon

1 to 12

Day

1 to 31

tm_mday

1 to 31

Hour

0 to 23

tm_hour

0 to 23

Minute

0 to 59

tm_min

0 to 59

Second

0 to 61

(60 or 61 are leap-seconds)

tm_sec

0 to 61

(60 or 61 are leap-seconds)

Day of Week

0 to 6

(0 is Monday)

tm_wday

0 to 6

(0 is Monday)

Day of year

1 to 366

(Julian day)

tm_yday

1 to 366

(Julian day)

DST

-1, 0, 1, -1 means library determines DST

tm_isdst

-1, 0, 1, -1 means library determines DST

Getting current time

To translate a time instant from a seconds since the epoch floating-point value into a time-tuple,

pass the floating-point value to a function (e.g., localtime) that returns a time-tuple with all nine items valid.

Example

Output

#!/usr/bin/python

import time;

localtime = time.localtime(time.time())

print "Local current time :", localtime

Local current time : time.struct_time(tm_year=2013, tm_mon=7, tm_mday=17, tm_hour=21, tm_min=26, tm_sec=3, tm_wday=2, tm_yday=198, tm_isdst=0)

Getting formatted time

You can format any time as per your requirement, but simple method to get time in readable format is asctime() -

Example

Output

#!/usr/bin/python

import time;

localtime = time.asctime( time.localtime(time.time()) )

print "Local current time :", localtime

Local current time : Tue Jan 13 10:17:09 2009

Example

import time

year, month, day, hour, minute = time.strftime("%Y,%m,%d,%H,%M").split(',')

see also

datetime Module

Example

8.1.4 datetime Objects

pytz Module

import datetime

dateutil Module

now = datetime.datetime.now()

print now.year, now.month, now.day, now.hour, now.minute, now.second

# 2015 5 6 8 53 40

You don't need separate variables, the attributes on the returned datetime object have all you need.

Date and Time

Files I/O

https://www.tutorialspoint.com/python/python_files_io.htm

Reading Keyboard Input

Two built-in functions to read a line of text from standard input, which by default comes from the keyboard.

The raw_input Function

The raw_input([prompt]) function reads one line from standard input and returns it as a string (removing the trailing newline).

str = raw_input("Enter your input: ");

The input Function

The input([prompt]) function is equivalent to raw_input, except that it assumes the input is a valid Python expression and returns the evaluated result to you.

str = input("Enter your input: ");

Opening and Closing Files

How to use actual data files.

Python provides basic functions and methods necessary to manipulate files by default.

This function creates a file object (fo), which would be utilized to call other support methods associated with it.

The open Function

Before you can read or write a file, you have to open it using Python's built-in open() function.

This function creates a file object (fo), which would be utilized to call other support methods associated with it.

file object = open(file_name [, access_mode][, buffering])

access_modes

File Pointer

Read only (default mode).

Placed at the beginning of the file.

Read only in binary format (default mode).

Placed at the beginning of the file.

Read and Write.

Placed at the beginning of the file.

rb+

Read and Write in binary format.

Placed at the beginning of the file.

Write only.

Overwrites file if exists, else creates a new file.

Write only in binary format.

Overwrites file if exists, else creates a new file.

Write and Read.

Overwrites file if exists, else creates a new file.

wb+

Write and Read in binary format.

Overwrites file if exists, else creates a new file.

Append

Placed at the end of file, if exists.

If the file does not exist, it creates a new file for writing.

Append in binary format.

Placed at the end of file, if exists.

If the file does not exist, it creates a new file for writing.

Append and Read.

Placed at the end of file, if exists.

If the file does not exist, it creates a new file for writing.

ab+

Append and Read in binary format.

Placed at the end of file, if exists.

If the file does not exist, it creates a new file for writing.

file object attributes

Once a file is opened and you have one file object, you can get various information related to that file.

Attribute

Description

file.closed

Returns true if file is closed, false otherwise.

file.mode

Returns access mode with which file was opened.

file.name

Returns name of the file.

file.softspace

Returns false if space explicitly required with print, true otherwise.

Example

#!/usr/bin/python

# Open a file

fo = open("foo.txt", "wb")

print "Name of the file: ", fo.name

print "Closed or not : ", fo.closed

print "Opening mode : ", fo.mode

print "Softspace flag : ", fo.softspace

file object methods

Method

Syntax

close()

fileObject.close();

The close() method of a file object flushes any unwritten information and closes the file object, after which no more writing can be done.

Python automatically closes a file when the reference object of a file is reassigned to another file.

It is a good practice to use the close() method to close a file.

Example

fo.close()

write()

fileObject.write(string);

The write() method writes any string to an open file. It is important to note that Python strings can have binary data and not just text.

The write() method does not add a newline character ('\n') to the end of the string -

Example

Acces

#!/usr/bin/python

Meth

# Open a file

fo = open("foo.txt", "wb")

Output of example

fo.write( "Python is a great language.\nYeah its great!!\n");

Python is a great language.

fo.close()

Yeah its great!!

read()

fileObject.read([count]);

The read() method reads a string from an open file. It is important to note that Python strings can have binary data. apart from text data.

Here, passed parameter is the number of bytes to be read from the opened file.

This method starts reading from the beginning of the file and if count is missing,

then it tries to read as much as possible, maybe until the end of file.

Example

#!/usr/bin/python

# Open a file

fo = open("foo.txt", "r+")

str = fo.read(10);

Output of example

print "Read String is : ", str

Read String is : Python is

fo.close()

tell()

The tell() method tells you the current position within the file;

File

in other words, the next read or write will occur at that many bytes from the beginning of the file.

Posit

seek(offset[, from])

Changes the current file position. The offset argument indicates the number of bytes to be moved.

The from argument specifies the reference position from where the bytes are to be moved.

from

reference position

beginning of the file

Examples

current position

position = fo.tell();

EOF

position = fo.seek(0, 0);

Renaming and Deleting Files

The os module

Python os module provides methods that help you perform file-processing operations, such as renaming and deleting files.

(import os)

The os module has several methods that help you create, remove, and change directories.

To use this module you need to import it first and then you can call any related functions.

Method

Syntax

rename()

os.rename(current_file_name, new_file_name)

os.rename( "test1.txt", "test2.txt" )

remove()

os.remove(file_name)

os.remove("text2.txt")

mkdir()

os.mkdir("newdir")

chdir()

os.chdir("newdir")

os.chdir("/home/newdir")

getcwd()

os.getcwd()

rmdir()

os.rmdir('dirname')

os.rmdir( "/tmp/test" )

Summary

File Object Methods

The file object provides functions to manipulate files.

file methods

OS Object Methods

This provides methods to process files as well as directories.

os file and directory methods

File Methods

File Methods Table

Method

Description

file.close()

Close the file. A closed file cannot be read or written any more.

file.flush()

Flush the internal buffer, like stdio's fflush. This may be a no-op on some file-like objects.

file.fileno()

Returns the integer file descriptor that is used by the underlying implementation to request I/O operations from the operating system.

file.isatty()

Returns True if the file is connected to a tty(-like) device, else False.

?????

file.next()

Returns the next line from the file each time it is being called.

file.read([size])

Reads at most size bytes from the file (less if the read hits EOF before obtaining size bytes).

*****

file.readline([size])

Reads one entire line from the file. A trailing newline character is kept in the string.

file.readlines([sizehint])

Reads until EOF using readline() and return a list containing the lines. If the optional sizehint argument is present, instead of reading up to EOF, whole lines totalling approximately sizehint bytes (possibly after rounding up to an internal buffer size) are read.

file.seek(offset[, whence])

Sets the file's current position

whence

default, absolute file positioning

seek relative to the current position

seek relative to the file's end

file.tell()

Returns the file's current position

file.truncate([size])

Truncates the file's size. If the optional size argument is present, the file is truncated to (at most) that size.

file.write(str)

Writes a string to the file. There is no return value.

*****

file.writelines(sequence)

Writes a sequence of strings to the file. The sequence can be any iterable object producing strings, typically a list of strings.

#!/usr/bin/python'

# Open a file in witre mode

fo = open("foo.txt", "rw+")

print "Name of the file: ", fo.name

# Assuming file has following 5 lines

# This is 1st line

# This is 2nd line

# This is 3rd line

# This is 4th line

# This is 5th line

seq = ["This is 6th line\n", "This is 7th line"]

# Write sequence of lines at the end of the file.

fo.seek(0, 2)

line = fo.writelines( seq )

# Now read complete file from beginning.

fo.seek(0,0)

for index in range(7):

line = fo.next()

print "Line No %d - %s" % (index, line)

# Close opend file

fo.close()

Files I/O